What is the most useful size as I’d like to try them?

Wow they've added more sizes since I bought mine. Don't think I would need anything
bigger than the 6.5". I use the 2.5 and 4.5 most often. It would depend what size block
you usually make. Pick a pattern and go from there.

I purchased a set last year and have been very happy with them! So far I've used the 2-inch and 5-inch ones. You can use a larger ruler on a smaller block, but not a smaller ruler on a larger block, so if buying only one, get the size just larger than what sized unfinished block you think you'd need.

Yes, they were a game changer for me. Love them!

What is it about the Block-Loc that makes it exemplary to others for trimming blocks?

The ridge along the diagonal fits securely against the diagonal seam of the HST, so it's not likely to slip and it's easy to measure accurately. You also only slide the ruler along that seam to change from one pair of sides to the other.

Love love them!!

Looks like something I need to find.

I love the conversation this thread has sparked!

Maureen NJ how do you figure how much fabric to make 8 HST?