I have used and continue to use a combination of the two. It's usually a cost-benefit thing for me. Some products are egregiously overpriced with poor quality, while others are amazingly affordable and will outlast me. I usually buy cuffs, for example. I can make them, but amazon has very affordable ones marketed to be used for weight-lifting and resistance machines. For the price, it feels silly for me to make my own. But for other things, like straps, rope, chains, locks, and various connectors and attachments, the hardware store is where I start. The thing about buying things at the hardware store is that it can be intimidating for some people. Knowing what to get can be overwhelming if it's out of your circle of comfort. And the products there are obviously not intended for bondage, so extra attention to any implications of using them for it is important. For example, when buying rope, there are a lot of different choices at the larger hardware stores, but many are not bondage friendly (they may be too abrasive, too stiff, be coated with chemicals for conditioning or protection, etc).
I don't currently own any dedicated bondage furniture, but I would probably make any if that time comes. I suppose it depends upon the piece and time constraints. As far as my favorite homemade solutions, the simplest sometimes impress me the most. An example that comes to mind is a quick 4-point hogtie with cuffs attached to double-ended snaps or quick links, each of which are then attached to one central steel ring (used in trucking and trailer rigging). I'm currently playing with the idea of making different adjustable straps. I love rope, but sometimes you can't beat a quick set up.