I used one and it worked great! YES THEYRE SAFE!
You can also rent one instead of buying. I think that through babybeats I paid $75 for 4 months use.
It worked for me at 10w1d. I tried to use it at 10w but couldnt find him. the next day I found him rather quickly.
They've got all sorts including ones with a digital readout. :)
BABYBEATS site:
http://www.babybeat.com/
Coupon code for %5 of monthly rental:
HP04
I started out renting mine and eventually bought it from storkradio. I love it! In my last pregnancy and this one, I heard it at 8 weeks. Just gives me peace of mind when I worry.
I bought mine off of eBay for about $125. First pregnancy I heard it at 10 weeks. Second pregnancy I heard at 9 weeks.
I rented one from babybeat. With my first i got the hb at 10 weeks and 2nd 8 weeks. They are safe same as doctors office. I had bleeding with my first so it gave me peace of mind. Good luck.
They are indeed very safe. It's the same thing doctors use at your appointments. I've never personally used one, but I wouldn't suggest trying until you're at least 12 weeks and beyond.