Well, 'any time I want' isn't entirely accurate at this point - I initally found it on Tuesay evening (which was the first day I'd dug it out - as I said, paranoia after last time) an then although I tried every day since, didn't hear it again until yesterday. I kept my cool, because baby is still pretty small and I have a large pelvis (apparently, so the gyne told me in April!) which means if baby is hanging out at the back I'm not going to find it. So, it would be very easy to get absolutely freaked out at this stage when finding it is hit and miss. Not to mention an anterior placenta can also make things tricky to pick up (grante at this stage most of us won't know if we have one).
Also, without an lcd readout it's quite possible for us 'lay(wo)men' to mistake the sound of our own heartbeat or the placenta (which is more whooshy sounding) for the baby. False reassurance is probably as damaging as no reassurance if the worst has happened.
Generally speaking, most posters on here are against dopplers for the reasons I mention and think it should be left to the professionals to use them. But I'm an old hand at using mine, and I can see that as my 'loss time' approaches that I would possibly be diving them nuts asking for fhr and/or scans to reassure me things were ok. Hopefully, I can take back a little control by using the doppler but by no means think it will replace their care (nor will I hesitate to consult them if I DO feel there is an issue).
Anyway. That said, I have a hi bebe bt-200. I bought it in 2009 from ebay!