I've used them, and they work well on simple, single line systems like rear brakes, but for an extra $20.00 you can pick up a decent vacuum bleeder, which, in my opinion, is much better at getting to pesky air bubbles that are reluctant to leave your system.
The speedbleeder site claims that you can get air into your system using a vacuum bleeder if you do it wrong, and this is true, but you can also get air into your system bleeding the old, "Squeeze and release" method, so the the solution is simple. Don't do it wrong.
Another trick I've learned, is to tap on places where air bubbles are likely to get stuck, (fittings, splitter blocks, etc.) with the base of a screwdriver, in order to "knock them loose". You'd want to do that when the system is under vacuum. On really difficult systems, like pain in the ass BMW ABS systems, I've even left the vacuum bleeder on overnight.
JC