I would never install delta - but that is my bias. I've never met a professional plumber who recommended delta but it's not like I've spoken to every plumber in the world either.

What part do you mean is plastic on hansgrohe ? For example, did you know that all the Grohe shower diverter trim plates are actually chrome plated plastic? I highly suggest at least going into a fancy showroom just to touch and feel the items even if you order them on the net.
I'm lucky in that I have a local plumbing supply that sells all the stuff at very similar price to the Internet so I get the best of both worlds.

Grohe is very reliable and very respected. many plumbers here like the valves. Hansgrohe is a brother company to Grohe - both founded by members of the same family. Hansgrohe is considered generally having the higher end product lines whereas Grohe has a lot of very reliable, home-owner priced sets. To save money I do have one shower that is not Grohe or Hansgrohe - bought the shower set on Overstock.com basically. Wouldn't you know it, I had to repair/replace the shower mixer after a year. It was under warranty but took up 2 hours of my time. The Grohe shower on the other hand - no issues whatsoever.

However, I have found several Hansgrohe lines that are similarly priced to Grohe. And some things you can mix and match whereas others you can not. For example, I recently helped a friend spec out several new bathrooms. All Grohe handheld shower valves and bars and handhelds. But for the "elbow" part that connects from the handheld hose to the wall water outlet, I suggested buying the Hansgrohe elbow instead of the Grohe one. The reason is for the same price Hansgrohe gives you an Elbow with a "check valve."

The plumbing inspector will definitely be looking for that check valve as soon has he/she sees that handheld and hose.

A picture of your open wall would be helpful to understand your dilemma with no room for a valve.

Is this for a Tub - or a Tub shower combo - or a Tub, shower, Rainhead and handheld combo, etc., etc...

If you choose more items - obviously the plumber has to connect more copper pipes off the shower valve to go to each separate thing you want. if he is limited with space - can you really have all those different items in your shower?

Have you considered having the shower diverter valve not in the typical location? The plumber can put the Shower diverter valve on a wall far away and even on a separate wall from where all the heads and handhelds are. this might solve your problem. For example, it's not uncommon now for people to have their shower valve control closer to where they can reach to get the water started and warmed up without getting wet - like on a totally different wall - perpendicular to the actual shower head.

For ideas and pictures - go to houzz.com and do a search for "showers" or make it more specific. They have thousands of pictures.

Kisu, you might be interested to know that a significant majority of Hansgrohe is owned by Delta. The two companies (Hansgrohe and Grohe) have been unrelated for a long time.

I agree with you about the quality of products these two companies produce, but I don't agree with your historical mischaracterization.