I don't use any brand in particular. I just get whatever they have at my Friendly Neighborhood Electronics Store (Orvac, in my case).
It's simple as pie and makes splicing look nice and professional. You slip on as much as you need, solder the two wires together, slip the tubing over the joint, then bake it with a heat gun (about $15 to $25 from the same store where you get the tubing). It's one-use only thing. To take it off, you slice it.
Itsabass, you know you can use a regular Bic cig lighter for that, right? As long as you don't melt the wire, it is easier and cheaper. Not trying to be a troll dude, just saying how I was taught to use it.
No, there are different diameters available. Ideally you will use the size that most snugly fits the wire. Guitars generally can use a skinny size for single wires and a slightly wider size for multiple wires (e.g. for extending braided pickup leads). But I usually get a variety pack, as the larger sizes are good for repairing cables.
Itsabass, you know you can use a regular Bic cig lighter for that, right? As long as you don't melt the wire, it is easier and cheaper. Not trying to be a troll dude, just saying how I was taught to use it.
I think the $20 investment for the heat gun was worth my while. Quick and clean, and easier to do in the control cavities. Plus it can also help to strip poly finishes.