This battery allows me to use my phone throughout the day without having to recharge, and have heavy phone usage demands. For work I make a lot of calls from my mobile, I also use the co-pilot live sat nav (best sat nav I have used and I prefer it to the built in device fitted in my car), I also listen to music and watch BBC iplayer on hour commute to and from work (download skyfire to be able to watch mobile TV and Iplayer). This battery copes with it all and I have 30%+ left to be able to call my wife to collect me from the station. One word of warning , I use an external battery charger and at under 12% charge left on the batter it takes seven to charge to 100%.
Although a little heavy for everyday use, if there is a need for an extended battery, this does the job. It takes longer to charge, as you would expect, but seems to last very well. I can't give any definitive figures, as I bought it to take on holiday, which I haven't done yet.
I purchased this battery because the HTC HD2's original battery would hardly last a day. Though not exactly what I would call compact this extended battery keeps going for about two or three days (depending on kinds of use) and as a bonus it comes with a very handy little stand. BTW, price was MUCH lower than in The Netherlands. All in all, a highly recommendable purchase.