I hate to swim against the tide, but I was given an original Pacemaker by a buddy that quit riding and had no further use for his. I've used it for the last 3 seasons without a problem that wasn't my fault. Mine uses AA baterries, not 9V (it's OLD), and I put a fresh set in for every race, but other than that, it's been fine. If I had a choice between that and the ProComp, I'd take the ProComp...it's a very nice unit (son runs one), but for the price (free in my case) the Pacemaker has been great. I wouldn't necessarily reject one out of hand if the price was right.
Tim H