It depends on the company I buy it from. Take Jetlasers for example. Why the hell would I get a 1.5W 462nm for 279$? Well, because their hosts are amazing and offer a temporary switch as well as a clicky switch. It has a key lock and led's for when the lasers armed. Aside of that it has a very nice focusing mechanism and overall their lasers have better beam specs than if you were to build one yourself.
Sure, building one by myself is going to be cheaper, but in some cases I'm willing to pay a premium in comparison for a laser that's overall just a bit better than what I would build. Of course you can make builds like these yourself too, but that involves quite a bit of time, patience and wouldn't be that much cheaper in the end.
Now, Jetlasers is one of the few companies that has such awesome hosts, so let me give another example. Take Dragonlasers. Their lasers are manufactured by CNI, making them of a quality that's not easily surpassed by building your own laser. Their hosts are simple, but solid and, in my opinion, look pretty good as well. Each and every one of their lasers has a low divergence, and depending on the wavelength a very tight beam as well. And, in the end, you won't have to go through the pain of finding a proper beam expander for most of their lasers.
This said, it doesn't necessarily mean that I'd rather buy a pre-built laser from one of these companies because it saves me work or anything like that. I find building my own lasers very exciting and rewarding, so it really depends on what I'm looking for in a laser when it comes to either building or buying it.