I upgraded to pro and really like it. From being able to do the pro workouts to being able to create unlimited workouts for myself. The $20 was worth it for me. I went pro back in January.
If you're not sure, maybe you don't need pro. The biggest thing for me is being able to create an unlimited number of workouts. That was the whole reason I purchased pro, and I knew ahead of time that I would use it. I find workout info in other places and liked being able to incorporate it into my own workouts on Skimble.
Another minor bonus for me is getting rid of the ads.
I also did the math and figured the cost of pro for a year, divided by twelve, considering how much a gym membership, or protein powder, or I dunno, goji berry granola and organic kefir, whatever it is I do for my health for a month costs, why the heck wouldn't I invest like 2 bucks a month in another tool if it's useful.