I think it's a case of "horses for courses", you wouldn't use plastic mounts in most laboratory experiments or in most applications in industry but you'd likely have access to a machine shop and/or an enviable project budget ;-)

It's very easy to be sniffy about things that actually work but are to a lower engineering standard than you'd like if you've never had to work without the financial and technical means you are used to.

Why not make a set of mounts in good old fashioned Meccano?
Now there's a serious engineering material ;-)

- Nick