I did mine with no issue. I had been flying ~250 hours a year in a twin engine airplane and made a couple attempts to get time in an RV12 first for familiarization, but it just didn’t work out.
I won’t downplay the importance of transition training, however, with 30+ years of flying in so many different airplanes, I think the RV12 is the simplest powered airplane to fly I’ve ever flown.
I do recommend heeding Van’s advice and not attempt “high speed taxiing”. Certainly go taxi around and do all of the ground testing and become familiar with the braking and steering, but when you decide to go fly, use the longest runway you have on a calm day and just go. A critical phase is at first lift off: stay in ground effect and manipulate the controls to ensure positive operation (better to find a problem near the ground), and then just climb out and follow the PAP. Easy peasy. If you think anything is abnormal on takeoff, just pull the power back and stop, go check it out and start over. If you feel pressured to go, then just don’t; phone a friend.
Here’s my first flight for some inspiration. Fast forward to ~8 min for the take off.
https://youtu.be/NjS8LDEWnPk
Note the ground effect control check. I didn’t go do the whole first flight as my wife wanted to be there, (which I don’t recommend), so I just did a quick trip around the patch to call it good and come back in to check out the airplane. And then did all of my flight testing after that.
I want to add that the hardest part for me so far has been getting slowed down for final. I am so used to coming in at 120KT and touching down at 95, so slowing to 65 and touching down at ~55 is so weird, but I’m getting there... the -12 will make you look like a rock star on landing squeaking the mains on and then you can old the nose off for a very long time (until ~41KT for me).