Rainne:
Which brand did you buy, how much did you spend (US $), where did you buy it from and do you like it? I have been looking on Ebay and there are so many options. Has anyone used the Hi Bebe BT-200?
Also, what week did you start to use it at & how accurate was it?
Thanks! 
I have the exact same one you mentioned. I bought it almost 4 years ago from amazon.com for $130. I've used it for all 3 pregnancies.
DS1= started using at 10 weeks, heard the HB then
DS2=started using at 8 weeks, heard HB at 12 weeks
DD1=started using at 8 weeks, heard HB then (super early, I know!)
Wish I would have seen this sooner to reply, but I hope that helps you!