The clasps on these is as tight as needed.  They hold up pants very well, don't dig into your body when you sit down and are aesthetically pleasant.  The adjustment strap is not very smooth, meaning it's not easy to adjust quickly- but after you've adjusted them to length once, you shouldn't really need to readjust them.

Updated 01-26-2012
Above is what I wrote soon after I purchased them.  By the way, I paid $6.89 for these when I bought them and $8.02 in shipping.  I complained to amazon about the cost of shipping as being unreasonable (especially if it's the only thing you order, then it just comes in a bag sent first class mail) and I think that helped bring the price and shipping cost down.

Anyway, recently one of the clasps has been sliding right off.  I thought maybe it was too taught so I put in some slack and it still unclasps (meaning the clasp is closed, but it comes off of my jeans).  I bought them 11-04-2011 so they have definitely lost some of the power in the springs.  I don't believe it's the jeans, because they are very light weight jeans.  Still a decent item though.  But I really hate paying more in shipping than the product costs.

Updated 03-11-2012
One of the clasps no longer works- it comes undone 5-10 times over an 18 hour day.  Downgraded to 2 stars.