In article ,
says...

http://www.harborfreight.com/cpi/cta...emnumber=46807

They aren't very good (I.e. this exact one from HF doesn't hold (in either
direction) with much pressure). I've seen the same made by other companies
which are much better (read: useable). They come in as many different
sizes as any bar clamps.

Ed

Same kind of tool: the Irwin Quick-Grip clamps. I've had some reversible
ones as well for a few years now, and I am generally well pleased with
them apart from the fact that the bars are not as rust-resistant as I
would like and that I dropped one off the bench and the side-cover broke
off. Other than that they've worked well as quick-clamps and also as
spreaders in cabinet assembly occasionally.

Clamping is reasonably forceful, the plastic/grips have not broken yet
(and I use them constantly) but I've managed to get the bars to flex
when using them as a spreader. Careful use advised in that direction it
seems.

Wouldn't dream of buying some cheap knock-offs. I paid about 10 times
the price of the item you quoted, and no regrets :-D

-P.