I am think about buying the Boremaster caliper,but i don't know if it is worth the money.So if anyone has used it would you please post.

I wouldn't buy it.
Mitutoyo makes a snap gage that reads from .4" to 1.4" for about $150 and it's a spring loaded dial indicator so once in the bore it will read and as you draw it out you can see the choke change.

Telescope gage works too

It amazes me that that tool is still for sale. It tries to do everything and does nothing well. The length of the jaws are too long for accurate measurement of wall thickness (there's a problem with deflection) and not long enough to measure a shotgun bore ( should be at least 15" to measure a 30" barrrel). You'd be better off with a regular bore gauge and investing in a wall thickness gauge that works, although they take some practice to use correctly.

And on that note you could build a wall thickness gage for about $75 in materials, and build it nearly any length you want.