Interior arrangement of shelves, bins, & drawers has a large bearing on usability of the space.

Top freezer fridges do make more efficient use of space.

Top freezer units definitely have more usable space in the freezer section. Those freezers are plain rectangular boxes. It can be easier to pack that kind of space with a lot of stuff.

With current bottom freezer units, however, several things combine to greatly reduce the usable space.

One is the protrusion covering the fridge's mechanicals which are located at the bottom in back of the fridge. You don't notice this as much on a top-freezer fridge because that protrusion is behind the produce drawers in the produce section. That protrusion is really noticeable when you are used to packing a freezer compartment in a top-freezer fridge.

A second thing that tends to diminish freezer space in a bottom freezer fridge is that most of them now have the freezer as a pull-out drawer and with sliding baskets rather than the old style of a swinging door. Like many people, I find the drawer-type much more convenient than the older swing-door type of bottom freezer, but that convenience comes at a price. The convenience of the sliding freezer baskets requires drawers within drawers with the mountings and rails (and sliding compartment spacing) all consuming some of the otherwise usable space.

A third thing I noticed when fridge shopping last year is that virtually every bottom fridge I saw had an ice maker in the freezer. If you do not use ice makers (and I do not), the device eats space. On some fridges -- and Kenmores used to be one of them --- the unused icemaker can be removed. Not so on others, though.

In my case, I found that going from a 20 cu. ft. top freezer fridge to a 22.5 cu. ft. FD fridge actually gave me more significantly more usable space in the fridge compartment and a lot less in the freezer section. While the fridge section's crisper drawers were indeed a bit smaller --- a consequence of using the same drawers that are used in the maker's models with the interior water dispenser where some plumbing sits behind the crispers --- I find that the full width deli drawer actually more than makes up for it. I find the large deli drawer is a great place for stashing the long things like zucchini, cucumbers, carrots and even romaine lettuce. Also, a good place for apples, too. Still plenty of room for cheeses and other deli-type items. This may not be the case with some bottom freezer fridges, though.

However, as noted, the usuable freezer space is a good deal less than the advertised numbers. My fridge was advertised as having 4.6 cu. ft. of freezer space. That turns out to be only a geometric measurement of the compartment without regard to the space that is actually usable. With the drawers and hardware and ice-maker in place, the usable capacity is more like 2.5 or 3 cu. ft.

The freezer space was no big deal for me because I have a large stand-alone freezer in the basement. It will be a different matter for others whose homes may not have a place for even a small chest freezer. Definitely a factor to consider in choosing any fridge with a bottom freezer design.

BTW, small chest freezers can be a great deal if you have a place to put one. They do not require much space -- a 5 cu. ft. model only requires a space of about 22" deep (front to back) by 28" wide (side to side). They use very little electricity, are nearly silent when running, and virtually all of the rated 5 cu. ft. is usable space. They are light and are easy to move. Regardless of the brand-name on the outside, most are made by Whirlpool (at the former WC Woods plant in Canada) or Haier (in China) or Frigidaire (??). As a result, almost all seem to be priced under $170.

As I say, a good deal if you have a space to put one but no help if you do not and get stuck with a too-small bottom freezer.

Excellent summary of the issue, JWVideo.
I had actually considered getting a separate refrig only unit for the kitchen and a chest freezer for the basement.

Truth in advertising would be a wonderful thing, wouldn't it. Well I guess the "space" advertised technically is true, but as you say, not even close to the actual usable space.

I agree with your frustration. What width is 20cf usually ?
I bought a used GE profile bottom freezer fridge because all of the fridges in the size I needed(33w) had ice or water which I cannot use or the freezers were to small(ie F&P). It has an incredible amount of room and it's not very deep so it doesn't extend outside my fridge cabinet.
I was so frustrated trying to find a fridge that had adequate produce storage that I bought an under counter KA fridge for extra fruit, miso, nuts etc. Now I have enough room in the GE for the produce. The door shelves are not those large bulky soda holders which gives it a lot more space inside too.
I wish these manufacturers would realize that there are many people who:
Eat vegetables
Cannot use water/ice due to concerns with leaks
And can't fit a 36"fridge

It does seem that us folks with small homes have been sort of relegated to poor design and few options.

I really don't understand the small vegetable bins. I like to eat a lot of fresh produce too, and sometimes luck into a bonus quantity that I need to store.

If I could have a do-over, I would have shopped for a new fridge (and sink) before I planned the new cabinets layout. I just assumed that I would find a fine 30" wide fridge to replace the 30" that I had . I would have been better off to sacrifice a couple of inches in my pantry to get a 33" wide fridge-- then I could have gotten a side by side (although aren't those supposed to be less energy efficient?).

Eatrealfood, a 20cf can vary from 30" to 33" wide depending on the model and manufacturer.