I had a real problem finding any good reviews of front-mounted child seats, so now that I've bought one I thought I'd share my thoughts.
Disclaimer - I didn't actually buy mine from Amazon, so I can't comment on their service/delivery/price/etc, but if you're here you probably already know whether or not you like Amazon. So onto the product...
We love our OK Baby Orion seat. It suits the riding we do. It fits my bike. It doesn't get in the way too much. My daughter loves riding up front. It fits nice and solidly, and feels safe.
The questions I had were:
Will it fit my bike? First have a good look at the fitting instructions http://www.use.okbaby.info/pdf_ciclo/LIB003R03EU_EN_ORION.pdf To fit the basic product you need about 20mm (measured at the back) of accessible head tube. A lot of newer mountain bikes won't have this. My 10-yr old Giant Boulder did have space, but the mounting block interfered with the centre-pull front brakes. The optional downtube-mounting kit works well for me, but it won't work if you have cables routed down the outside of the tube. If you don't think that this seat will fit, I have a friend who loves the Weeride, so you could always look at that.
Will it be safe/comfy/practical for my daughter? Yes. My daughter is 17 months and a little over 10kg. The seat fits her really well, and she's nicely secured by the ankle and shoulder straps. There's no slipping or unsteadiness. She loves the view and I love the fact that I can see what she's doing. I can point things out and chat with her.
Will it be comfy and practical for me? Yes - mostly. I'm a tall bloke so it does require a slight bow-legged ride to keep my knees from hitting it. We normally only ride for 10-15 minutes to and from nursery, and our longest rides are only an hour, so the riding position isn't a big issue. Getting on and off the bike is easy, and I can still swing my leg over the back wheel, impossible with rear-mounted seats.
Niggles: generally this is really good, and I'm very pleased with it. Two things are tricky though: To release the shoulder straps you need to pinch the front and back of the snap fastner together. It's hard plastic and awkward to manage, especially if your little darling wants to be out and is starting to wriggle. Also, it should be easy to remove the seat from the mounting block, but on my seat the clips are awkward and stiff. Neither is a big deal, and I still think that this amounts to good value for money if you're set on a front-mounted seat.