Honestly, I love my factory one. I know people without them don't think they're big enough... I've also known many people who did aftermarket ones... I don't know anyone who hasn't had an aftermarket one leak. And at some point, the installer is either out of business or tells you there's not warranty on it... And you end up gooping it all up with silicone....
I would ask the installer a TON of questions... Ask for references and then actually talk to them. Look at other work the installer has done. Seriously... I know it sounds like a lot of hassle... but I'd hate to see all that silicone goop on my roof after I forked over $1200!!!
