Op, if you're still reading this, he's bang on the money.
Posters on here sometimes say the trade people on here are out to rip people off, overcharge, spec kit that's 'over the top' etc...
The truth is, Yale is tat, plain and simple. You'd get the same level of protection going onto ebay and buying two dummy sounders
from someone like Elmdene or Pyronix, or even a broken Yale just for the bellboxes. There is no decent system at £160, and the
ones there are, are no better than a dummy.
Basically, I appreciate you might not have £500-700 - so please don't waste £160!