Inside Sun - Whats the catch?

People sell that kind retrofit under a lot of different names and with a lot of different parts. I'd look at the parts, there's a standard mogul base, a reflector (batwing lol, first time I have run across that one) and a ballast of unknown description like sostoudt mentioned which would be the thing I would watch out for or want to know more about, too. Then there's the bulb which is a Slyvania 400W at 20K or so, I haven't heard of people running a Slyvania bulb but if it's 20K or whatever why not? You can replace it later with whatever you like, as someone else also mentioned.

Keep in mind this is a retro fit kit even though they are selling it slightly differently, again like others have also mentioned you will need a splashguard/UV filtering lens and probably a housing for the whole light etc. cause that will get hot, as well as a suspension system.

At that price, for that equipment with some unknowns out there, it seems like kind of a gamble to me.