A week or so ago there was a thread asking for advice on how to prevent a batter from dropping her hands. I do not know the official name of this device or who makes it, but our players have nicknamed it "The Blue Monster". It is great, but I would recommend using an old "beater" bat with it!!!
Not a fan either... it teaches a downward path swing. Some people swear by this style, and to each his own, but I think good old fashioned long tee work will do the trick for a ton less money!
I don't think it is a good training tool. I would consider the following less expensive, easier to transport ideas:
1. A deep tee slightly above knee height and just below armpit to teach getting on bat plane early (try to hit line drives up the middle).
2. A string 40' long with a wiffle attached. Mount one end the height of the pitchers hip and connect the other end to various heights in the strike zone. Practice staying long in the zone with the barrel following the string.