Excellent products IMHO. Have used many of the "polymer sealant" type products, and Autoglym may be my favorite.
Surprised to see someone say it wasn't easy to buff off because I found the Autoglym products the easiest of all to buff off (using microfiber). Much easier than Klasse, for example.
BUT you have to be careful not to use too much product. A quarter size "splotch" on an applicator will probably do a half a hood or roof, at least.
ALSO you do have to let the Extra Gloss Protection dry a MINIMUM of one hour--an hour and a half is even better (the label states one-half hour to an hour, which is a little optimistic in my opinion). If you let it dry long enough removal should be easy.
The instructions on the bottle aren't as explicit as the instructions at the Autoglym website. Also CMA has some application tips at their website. Follow those instructions, and there should be no problems, should you decide to use the Autoglym products.
Also--as others stated above you do want to keep it away from vinyl, unlike some other products. I don't find that to be a problem, but some people do.
I use the Super Resin Polish twice a year--you can't layer the Super Resin Polish. You CAN layer the Extra Gloss Protection. Like other products of this type, it helps if you layer it, IMHO.
Durability:I applied about four layers of Extra Gloss Protection over a period of a month or so; the last was in late November. I'd say I got about three months and some change of good protection and shine that way (it was a very mild winter up here this year, however.)
The products do have a pronounced "chemical" smell. However I suspect most products of this type would have a very "chemical" type smell, if some type of fragrance wasn't added to them. The smell doesn't bother me--I'd rather have the stuff smell like what it actually is, rather than smelling like chocolate, cocoanuts or cherries. Seems a little safer that way.
I've also used some of their other products--I've used the vinyl protectant on tires and like it a lot--very reminiscent of 303--never used it on the interior, however (the only protectant I'll use on the interior is either Zymol Treat or Pinnacle--everything else is too glossy and slippery for my taste--even 303)
I also like the Glass Polish. The only Autoglym product I DON'T like is the car wash--very little sudsing. Although it seems to work okay for removing dirt and leaving the car looking nice, the lack of suds bugs me. I wouldn't recommend it.
Here is a prior thread regarding Autoglym. It got the "Ron K seal of approval" which indicates to me that the Autoglym products are safe and use good quality ingredients (even if they do have a "chemical" smell).
http://216.147.22.29/forum/showthread.php3?threadid=1933&highlight=autoglym