I have not used one of these kits because I make my own. However, there is no reason that a kit wouldn't sound just great as long as they have used good tone woods such as rosewood, walnut, sapele, mahogany, maple, koa and a few others for the back and spruce, cedar or redwood for the front. In a kit, the neck will probably be mahogany which is good, but it is important that it be quartersawn (vertical grain) or there will be bowing of the neck even with a good rod inserted.
If you are getting a kit that has a radiused top, the neck should have the appropriate angle for mounting the neck but make sure you check the reviews of the kit to see that this has not been an issue.
One thing to consider is that your first build of a guitar (or ukulele) will show you where the challenging aspects of the build will be and it might make sense to start with an tenor ukulele kit for practice. You can start with an inexpensive kit from Stewmac (Title: StewMac Ukulele Kits | stewmac.com) where the kits are currently on sale for $89 for a tenor uke. This would give you a lot of training and the process of building an uke and a guitar are very similar.
For an acoustic guitar, I would probably stay away from eBay because of the shortcuts that are often taken - mostly not using quartersawn stock for all the components where it is necessary.
Good luck! It is really fun and a great way to take your woodworking skills to a new level. Please feel free to ask whatever questions you may have. I don't consider myself an expert yet, but my quality has gone up dramatically since my first build.
Stewmac is to lutherie as Amazon is to general merchandise. Their quality is excellent and their service is outstanding. It is not an inexpensive hobby, though. As I have shown to others, though, you don't have to have all the tools and jigs that you can buy. It is a hobby that you can do with limited tools - especially when you can buy any component (neck for example) so you can build the components you are prepared to build and buy the rest.