Hey hunni, I got two, an Angel Sounds one I bought outright from Amazon which has been superb have heard HB since 9 weeks - the only downside for me is it works on headfones so have to call Noel to listen and by time he got to me bubs has moved - but overall it is good. Cost me about £25.00 plus postage
I also rented one from Anawiz - a HI-Bebe which I couldnt get anything on till about 14weeks. This is good but you do have to press hard. This costs me £19.99 per month but its mine after 6 months - you can also rent it for approx 12.99 per month but have to send it back when finished. I like this one cus it has a loud speaker so everyone can hear when hb found.
Personally if you want reassurance early I would go for the Angel Sounds then maybe get another as times goes on if you really want to....
xxxx