I decided to go with the real Definitive brackets figuring they were made for the speakers. Good choice.... they stay put where you tighten them. I have had them up for 3 weeks and they are still perfect so I bought another set for the other pair.
Vtech did a good job with this phone. It sounds fantastic. Not a lot of bells and whistles, but what can you expect for this price? It does what it's supposed to cheap and my neighbors can't listen in!