When in Blinky Mode the Tekin and Juststock setting choices are about the same. The only capability you lose with the Juststock is that it cannot run boosted timing. If you are in the US this is no loss as we are all Blinky.

I was racing a few months ago in 17.5 Blinky sedan and I connected my Tekin RS Pro backward. That killed it. In order to keep racing that day I got a HW Juststock for $50 from the local hobby shop.

I put it in and in the next qualifier I turned the EXACT SAME lap times as I had the previous run with a $229 speedo. After getting my RS Pro repaired I put it back in my car and had no increase in performance. I ended up selling my Tekin and running the Juststock because it was smoother and I feel the Juststock (and all HW Speedos) are faster in motor start up than the Tekin. I can get holeshots at race starts that I could not get with my Tekin's or my LRP's.

If you are running in a Blinky Spec class (10.5-25.5 motors) I would say you can run the Juststock at any level with confidence.