In brief,
A very well made, adjustable and very simple but very effective Grip / Swing training aid designed, I guess, primarily for indoor use but can be used just as effectively outdoors.
The aid comprises a Shaped Rubber Hand grip affixed to a cranked metal shaft, about 18 inches long, terminated with two detachable / adjustable metal weights. The idea being that the shaped grip ensures that your hands always grip the "Club" in an identical and correct position - thereby training them to this position ... The detachable weights simulate the weight of different clubs and allow you to Exercise and strengthen your grip, wrists and forearms etc. The club is then swung - hopefully on path and plane, as a normal Golf club, thereby promoting yet more repetition and muscle memory.
Remember "Practice makes permanent, not perfect"......

Now what's it like in use?
I like this piece of Kit.
I suffer from Osteoarthritis in my hands and wrists, amongst other areas, so the ability to use it indoors every day - WHAT EVER THE WEATHER, and with varying weights according to how I feel is fantastic. Not only does it let me practice my swing everyday, but it also helps me to keep my Back, neck shoulders wrists and hands in working order and to maintain suppleness. If you also suffer from this type of ailment, you will understand what I am saying.

I use the aid in conjunction with a full length mirror so that I can see all angles and check all parts of the swing at all times. As the item is basically a shortened club you are able to check your Takeaway, wrist cock / set, swing plane, shoulder turn, club position at the top, downswing, whether you are casting at the top, late hit, follow-through etc, etc, etc. In short all aspects of the swing can be practiced and checked.

The two detachable weights allow adjustment so that you can work simply on swing or strengthening or both, the choice is yours. All of the weight can be unscrewed from the shaft if you want to swing the "Club" very light, or you can simply unscrew what I will call a "Secondary" weight, from inside the Main weight, thereby roughly halving the weight on the end of the shaft. It is very flexible allowing you to "Tailor" the aid to your requirements.

Time for the usual proviso now, don't think that this swing / grip trainer will improve your Golf swing overnight because it won't, it is just an aid which, when used in conjunction with normal practice routines and work / lessons with you local pro, should be of benefit your game.

If you swing / practice badly with it, then you will swing badly on the course with your normal clubs, it is not a "Fix all". Use it at home when the weather is cold and you can't get to the range, and use it outdoors at the range when you can - It is well worth the effort. If you use it for exercise as well, like I do, then you get double benefit.

Any niggles?
1) I have only ever seen these for Right handers, I don't know what you "Lefties" are supposed to do? - shop around to see if someone does a Left hand version I suppose.
2) Occasionally the inner weight can become a little stiff to undo from inside the main weight body.
3) The grip can twist a little on the shaft.

All in all this is a great little aid which should help your golf swing, as long as you use it correctly.