I've been using one on my Savage 10FP for about 5 years. Back then I had to email them to get one. (They hadn't started selling online yet.) It installed very easily and is easy to adjust. The price was a big selling point too. I'm not a Marine Scout Sniper or LEO sharpshooter, so I don't need a top of the line unit. Just something that works good and didn't break the bank.
I have run one on two different rifles so far, and have had no problems with them. They are relatively cheap and easy to use. They work well under a stock pack also.
I don't have experience with the Brownells piece, but I have just installed a Karsten. I love it. Easy to put on, solid, and looks good. Service was quick too.
Just fitted a Karsten onto a HS Precision stock and its completely transformed the rifle. Straight forward to install and very sturdy once in place (I got the model B). A very good option for the money (and that's even with international shipment, duty etc!). Karsten is also great to deal with.
Karstens' cheekpiece is very nice. I have installed four. They are fairly easy to install and will give you a very comfortable and solid cheek weld. Karsten offers several versions, I like the version that has notches and flush mounting hardware.