I started off with the smaller version to try it out after seeing it in use in some cardmaking tutorials on Youtube. I really like it. Beware that the SU Clearmount stamps, even without using the stickers on them, don't work well on this block. My SU Hello Daisy stamp will not stay stuck to it at all and I end up using one of the cutting pads from my Big Shot for this stamp since it is so large. I do find the grid lines really useful. I might splurge and get the bigger one at some point.
My favorite go to acrylic blocks are the ones made by Inkadinkado like these ones:
Inkadinkado Clear Block - 1PK/Extra Large*: stamps*: stamping*: scrapbooking*: *Shop | Joann.com
There are a couple of different sizes. I like the wavy edges which make them very comfortable to hold and the grid lines for helping me line up sentiments and image stamps. I have a couple CTMH and SU acrylic blocks and they're nice and thick, and great quality-wise but I would prefer they have the grid lines etched right in them like the Inkadinkado blocks. Both CTMH and SU sell a type of cling grid-line stickers for these blocks but from what I've read, they don't stay on very well and people find them annoying.
I might try some Apple Pie memories round ones next but they're not quite as thick as the Inkadinkado blocks.
Acrylic Stamp Block Round Set of 4*: stamp blocks*: stamping*: scrapbooking*: *Shop | Joann.com
I have some really cheap thinner blocks and I don't like them at all after using the thicker blocks. They feel wobbly and just aren't substantial enough.
I hope this helps with your selection