I don't think there are many of them that are scams (did I really just say that).
Whether they are very effective is a different matter. From the reviews I have read for most of them, it seems that they come out fairly neutral, which is a lot more than can be said for most racing systems.
In terms of individual pieces of kit, I can't really say as I have not used one. I have been looking into it though and have read hundreds of reviews. Nothing comes out that positively but join the T2W forums and read their software section. As usual though it is full of cynics who condemn stuff without ever having used it so you will need to sift out the useful comments.
I've never understood the attraction of bestiality but looking back over my life it does appear as though I married a cow, lived with a moose, been out with at least 5 dogs and spent a lot of time being chased by whales.