A speed oven is like a convection microwave, in that it combines heat with microwaves. The exact difference between a speed oven seems to be a matter of debate - some say that a speed oven can both microwave and heat at the same time, but some products described as convection microwaves can also do that.

We decided that a speed oven could not replace any of the appliances you listed.

We use a microwave primarily for thawing frozen stuff. We make stock in bulk and freeze it for later use, and we use stock often during cooking, so we need a separate microwave.

A speed oven is not as big as a regular oven, so most folks still want a regular oven.

A speed oven cannot make toast as well as a toaster.

Of all the items in your list, the toaster oven is the nearest to be replaceable by a speed oven, but even that depends upon how you use the toaster oven and exactly which speed oven you choose.

All that said, we are still considering getting a speed oven, because it cooks small to medium sized dishes very quickly, using very little energy. It's just an "as well as", not an "instead of".

Of course, as always, YMMV.

I think to be a true speed oven it needs to be 240V and have selectable modes that mix both microwave and convection/broil methods. For instance, we have a Sharp convection microwave in our motorhome that can do one or the other mode; it runs on 120V. While handy, it simply is not in the same league as our Miele.

Our speed oven serves as our second oven, but when I am simply baking one dish, it usually goes into the speed oven because it is the most convenient and doesn't heat up the house like our big range does when we crank it up. And it is pretty fast if you use a combination mode.

We do not have a second microwave (well, we do, actually, but I keep it in the garage for emergencies) and that presents a problem. When you have a dish baking in the speed oven, but somebody wants to reheat a cup of coffee, it is a pain having to pull the dish you are baking out, carefully, since the oven is hot, then carefully put in a coffee cup for 30 seconds. Anyway, it still works okay, but it's an inconvenience at times.

I never use a toaster oven, never owned one, can't comment. I do know you can toast the bejezus out of a tray of English muffins or bagels if you are trying to get a lot of toasting done at once using the broiler element in the Miele. But that is a low demand function here, we get by fine with our toaster.

I consider our speed oven a different animal which i am still getting used to. the biggest pain for me in switching between microwave mode and speed oven mode is the pans. otherwise its a great microwave. the speed oven can be for dummies or it can be a very useful sophisticated oven. i like that it puts everything on a timer. ours is also an excellent warming oven.
doesn't replace a toaster but makes good hot sandwiches.

Although a speed oven will usually do the 4 things you listed, (three if you don't count toast twice), I would not say it is a replacement for those.

As an oven, it's to small for some dishes.
As a microwave, it can be more cumbersome to operate than the place push models most are using.
Toaster ovens are usually fairly inexpensive.
And, what if you want to use one function but are already using another function, i.e., You want to warm up your coffee using the microwave but are cooking something like quiche.
IMO, a speed oven is a versatile way to accent the other products you have in your kitchen, not to be used in lieu of.

Most high end speed ovens are designed to offer a unique combined energy system for improved meal quality. Trying to produce a four in one amalgam of different appliances with comparable performance to stand alone items was never a priority.

I agree with Laat2. The speed part is the crucial one. What sets them apart is the ability to roast a chicken in half an hour or a potato in seven minutes, with no loss in quality from going faster (I'm not so sure I believe that in practice, but results probably vary from brand to brand--I would never ever eat chicken "cooked" in a Microwave (I've pushed it around the plate when served) but the chicken on the speed setting of the Advantium is okay. I can do better in a real oven, so far, but it's fine). That's also partly the 240 V. I think when there were more 120's, they said the 240 was four times as fast or something. Check the GE website--they sell both.

I chose the Monogram Advantium Pro because it really is as large as an oven. It can fit a 16" pizza pan or a 17.5" Pyrex baker (the latter on the wire rack). Most of the time, I use it for small microwaving tasks. I rarely use a microwave while entertaining, so the Advantium is perfect for a third oven. I don't have room to store a portable oven. It doesn't do everything a good oven can do, and while it's a great choice for an RV, otherwise I wouldn't want it to be my only oven. It's convection only, on oven mode, so one is limited thusly.

When I chose it, I also thought I would be using the speed feature a lot. Circumstances have changed and slow is almost always just fine. It's the speed where the big bucks go, however.

Some in the forum warn that using a speed oven primarily as a microwave isn't at all cost efficient, as it is an expensive appliance and the more you use the MW the quicker it's guts degrade and eventually fail.

As far as I know, only the Miele claims to broil, and at that the reports are that it doesn't do it as well as the regular oven. If you use your toaster oven for small meals, and you don't need a strong broiler (which some toaster ovens have for toasting things), then yes, it can replace it. Some people do find that their speed ovens take a long time to preheat compared to their toaster ovens, however.

Of all the speed ovens, I believe the Advantium makes the worst toast, though some people think it's okay. I think it's really bad.

Summary: Yes, a speed oven can more or less take the place of all the things you've listed, and does in some high end motor homes, but, like most combo machines, that's with some sacrifice. Lots of people use one as a light duty microwave and second (or third) oven, besides the speed features, but the speed is what it does best.

i think that in decades from now everyone will wonder why it took decades before speed ovens became the norm in every house.