Using a guided system for your sharpening is like riding a bike with training wheels. Yes, it is "more precise and repeatable" but... it's not very rewarding. And you don't learn the skills you need to really bring out the best in the craft. If you really want to understand sharpening and get the best edge you can, freehand is recommended. Take those training wheels off. yes, you will fall off, but you'll be better at the end of the day.
And just like riding a bike, it does not take 20+ years. Yes, you always get better, but that's why it's an art. And anyone who has been freehand sharpening for 1 year can put a better edge on a knife than most people with a guided system because they have a better understanding of pressure, following angles along curves, and moving up in grit by feel and sound. You can't get a good sense of those things with a guided system. So there is a lot more to sharpening than just angles.
A few thoughts keep popping back up every time this discussion comes up.
What do you do if you should need to sharpen something away from home/unexpectedly?
What do you do with a hatchet or machete? I believe some guided systems can do machetes, but how long does it take? Can any do a hatchet or axe (or grass hook, sickle, etc) and how long would it take?
What about finishing an edge/reducing the burr? I have no experience w/guided clamp systems, but it seems like it would get very tedious switching sides to work on what is, ultimately, a consumable tool? Sharpening tools is a maintenance chore, it cannot be done once or twice to perfection and you're finished.
What about maintaining/ altering edge geometry - grinding or thinning a back bevel has to be extremely tedious also.
Haven't people sharpened tools for a couple thousand years without guided systems - why have they only cropped up recently?
I can see where it might be nice to have for a knife that's just for display, but for a working tool I cannot imagine being tied to a machine. Then again, I have never owned a guided system so what can I say?
I would only do my laundry by hand if I had absolutely no choice where some folks might enjoy beating clothes clean, so perhaps there
are comparisons I can understand....
Should I free-hand, use a rock, washboard, front loader, top loader? Too many choices!
Its all good whatever you use but even so, just out of academic curiosity one should study free-hand - it can only help ones understanding in general (and you might have to sharpen a hatchet someday).