Aye, undertrays can be a bit of a faff, but I think I'd still rather have them in place - just make sure the garage puts them back after carrying out work!The underside of the car is pretty "slippery" with undertrays etc much in evidence:
A bit of a mixed blessing in my view as they tend to restrict access for things like oil changes and repairs However, being under warrant for the next 3 years, that's not so much of a concern to me. By the time the warranty expires I'll be 80 and maybe not "doing" cars any more anyway!
I had a Mazda with useful cut-outs in the undertray for access to essential bits - if you had tiny hands!
Citroen always used to fit full-length undertrays - even my 2CVs had beautifully smooth slippery underbodies, despite the appalling mess going on up top