Builders best friend. No need to hunt through piles of lumber for straight, 2x4, 2x6 lumber... This "TWEAKER" will allow you to make the necessary adjustments to bring any lumber into line.
Whether decking or framing, This has the pull you need.

The Short of it:

If you only have the money for one tool, skip this one and purchase the Stanley Fatmax. It comes in two sizes, and is a much better made tool for similar money.

The Long of it:

The finish on the Tweaker identifies it's "Made in Taiwan" construction (i.e. poor); and, as pointed out by others, the inner claw is too small to obtain a firm grip if you have a really stubborn board to deal with. I do like the apparent ability for this tool to be hammered into tight places for prying; and the "handle" would lend itself well to extension with a piece of metal pipe for some real prying assistance.

However, I am not sure of the quality of the metal, so any "assistance" applied as I indicated above (i.e. hammering, or using a pipe for an extended handle) is at your discretion. I find that any tool "Made in Taiwan" seldom stands up to 'normal' use, let alone going above and beyond.

The Bottom line:

The Fatmax is able to handle thicker stock, for the heavier joists and such. It is a much more finished tool, and I would not be too worried to add a little "assistance" to it to get a job done.
If you have the money to purchase several tools, there are some functions that this tool may perform better then the Fatmax, so go ahead and get one. I did. Nice idea, but I think I would have skipped it if I had seen it close-up before I bought it.

Works pretty well for holding things straight, leveraged by one knee so I can get a few nails in place. When you work alone you occasionally need a third arm.

This tool does what its made for. It works very well for straightening twisted studs. Basically for 2x4 or 2x6 lumber anything bigger and it doesn't have the grip necessary to straighten.

I've always used homemade versions of the tweaker out of wood and thought it was time to try the real thing. It works ok, but the handle is too short to lever the worst 2x6's around without getting some unneeded arm exercise. If it was maybe 6-8 inches longer and a little lighter and still sold for the 30 some bucks, then I would be impressed.