My surprising experience with sidesaddle was that it really didn't take long to get very comfortable lag putting. Early on, hitting longer putts without looking at the ball scared me a little. But I got the hang of it pretty quickly. It helps that you really don't need to keep your eyes quite as "fixed," in the sense that I could start my backswing while looking at the hole and then look down at the ball on the thru swing to ensure solid contact while still having a very clear vision of the hole in my mind.
But I struggled a bit on shorter putts. It just felt like my head was too far inside the target line to get really consistently excellent aim. But I also suspect my sidesaddle putter was a little too short for me - I purposely chose one on the short side to make sure it would fit in my flight case...
I abandoned it pretty quickly given my confidence putting conventionally, but I gotta say, I've been shocked that it hasn't proliferated on Tour in the few years since the anchoring ban. Even though I didn't adopt it long-term, I definitely found it to be a valid, easy-to-adopt, and effective way to roll the ball, especially if using a well-fitting putter built for the purpose.