as im sure you will see the bulk of the pros onthis board (including myself) will strongly disagree that that type of system is a good one, IMO it gives a false sense of security. There is much more to that unit being made complaint with 50131 than the things you suggest and i dont think the hardware is caperble of being compliant.
as you have said the powermax is a fine product and is well priced. The std bell is a fully wireless bell on the powermax not a powered one but a powered one is available.
If you were to install one and see what a real product is like i doubt you would still recommend it. While im sure they do have a market I find it difficult to see how you can say how great they are when it is all you install. If i installed telephone systems and only used wet string and yoghurt pots then id think that was the way to go (cheap you see and better than nowt) but as hod no experience of a telephone i couldnt compare.
My biggest concern is that some of these systems seem to use the bellbox as the panel. ie outside totally unprotected etc.
But im glad you like them and hope one never fails to perform and you get held accountable.
James