I'm sure you'll get as many opinions about this subject as members on this forum. For what it's worth, I've used this product on my last seven vehicles, and without going into a long song and dance, I think it's great. The only other thing I do is run my vehicles through a carwash when they get dirty. After 6 or 7 years my vehicles still look like new, and I live in a snowbelt region with well salted roads in the winter. http://www.tst5k.com/tst_5000.html
Hers: 2008 Jeep Compass Sport
Mine: 2014 Jeep Grand Cherokee Overland V/6 ORA II
Michelin LTX M/S 2's
Depends on what they are trying to sell. Are they trying to sell you an $800 paint protection package, or a $20 bottle of Mopar sealant? If the latter, sure - use it. DIY. Your paint does need protection, and in general, sealants last longer than waxes. There of course are a few exceptions to this rule.
Depends on how the warranty works. With my GM products, I often purchased Auto Butler paint sealant. But only because you have to bring it in every 6 months for inspection, at which time they reapply - clean and detail the entire vehicle exterior. For the $300 price (exterior only), it was like getting a bargain detail 2X per year. I usually scheduled my visits in the spring (to clean off the winter crap) and fall (prepare for winter).
Now, if it is just a 1X application at new - I would never spend the money.