The every 1/2 inch one is more useful, but more flimsy, as others have said. That flimsyness can make it dangerous. I was using mine when the plastic strips shifted and the cutter jumped out of the slot. Because I was putting weight on the ruler, I couldn't move my hand quickly enough and I lost a chunk of my left index finger. 0/10, do not recommend. (Losing a chunk of finger, that is. The ruler I'd rate at about 5/10, and I'm glad to hear that the Stripology is sturdier, as my JT one is about to be retired.)

I agree with Sephie. The Creative Grids stripology ruler is pretty sturdy and will cut on half inch increments whereas the June Tailor only cuts on the 2 1/5 increments. IMO paying that much for a ruler, I would want one that would do more than a few cut sizes. Unless you do cut a lot of jelly roll strips or charm squares from the same fabric. I have the CG Stripology and Stripology Squared. I made a shadow box quilt and was able to cut all those 1 1/5 strips in no time with the Stripology. When I made my jelly roll rug, I cut all the strips using the Stripology. Easy peasy!!
Creative grids has videos on youtube describing how to use. Maybe check one of those to see which strip cutting ruler would work best for you.

Murphy-there are several different kinds of JT rulers, some of them cut 2 1/2" increments and others 1/2" increments, they also come in different sizes.

Safety is very important with the slotted rulers no matter the brand. I used a Quilter's Slidelock on top of my rulers when cutting. I had a bad cut before and all it took was one for me to know it could happen again.

I previously posted on this thread about the June Tailor ruler being so flimsy. My JT "Shape Cut" ruler has cutting slots every half inch. That doesn't make it any better. Mine is a couple of years old, though.
bk

I just bought the Quilter's Slidelock on Amazon. Between that and gloves I will hopefully stay out of the ER!!!
I've never had a nasty cut but I've probably just been lucky. I've heard a lot of horror stories here.

Yes, you are correct that the JT rulers do vary in the increments they cut depending on the ruler. In the size that the OP said (20 x 23), I've only been able to find one JT ruler of that size and it cuts in 2.5in increments. Have you seen one of that size that cuts in 0.5in increments?

As I do not own a JT ruler and only own a Stripology, I can only say that the Stripology is awesome. The thickness makes me feel confident my cutter will never slide out of the slot and it never has. The material it's made of is also pretty sturdy and stiff but I do still store it flat. It also comes with instructions (easily Googleable) on how to cut strips of a 0.25in increment easily - it has a chart for some common sizes but if you need an unusual size, the math is pretty easy and the procedure is the same. Unsure how easy it is to do that on a JT ruler slotted every 0.5in?

I have the long and short one. I use the long one to smooth out my quilt layers when glue basting. Works great. I use mine on top of the ruler not in place of. Wasted time and steps to use in place of the ruler. Makes no sense at all. The ruler isn't budging anywhere with the Slidelock on it. Before the US company got the okay to make it, I was sold out of Australia and the name was Rule Safe.

Thanks for the info, Onebyone. I also like glue basting so your tip will be a good one for me. I looked on Youtube to see how to use it and will use it on top of rulers, not instead of. I got the larger one but will probably get the smaller one as well.
Can't wait to get it!