If you are buying the hot tub and the cover from the dealer, the cover lifter installation should be included. I know that some dealers don't and I find it very annoying. I've had a few hot tubs in my life, and recomend having the dealer install it.
Can you install it yourself? Sure. But it can be a bit of a pain. and can take you 1/2 an hour maybe longer to do, and you run the risk of not installing it correctly, and damaging the tub, and/or the lifter.
If the dealer tells you it's "no big deal" then, if it's not a big deal, have them install it. A seasoned dealer should have templates and jigs to help align the lifter and install it correctly and can do it quickly.
The Prolift ii has the gas shock assist in the back and is a great lifter. I don't get why this dealer is trashing pro lifts, not installing them and seems to be steering you away? Why the Porlift over the Prolift II?
If you are on a tight budget, then the dealer recomending you lesser price d, quality units then I can understandbut if the extra $150 is not a big deal to you, then I don't understand why this dealer would not recomend and install the PLII? It's the better of the two lifters imho.
When you ask him directly specfically why he doesn't like the lifter, what does he say?
I have had great luck with my PL II and highly recomend it.