I think there’s a happy medium somewhere in between. I’d say you want to go a bit larger than a 20" unless you’re learning in a gymnasium or somewhere else with a perfectly smooth floor.
Larger wheels have a bit more rotational inertia that helps especially if the surface you’re riding on isn’t perfectly smooth.
I mainly use two freewheel unicycles: a 24" and a 29". I only “coast” (or try to), I use the brake to get on the unicycle and to stop.
I find that the 24" is a good size for learning in a gym on flat ground. On the other hand, outdoors, a 29" offers a lot of stability. This morning, I rode the 24" to work; it’s harder than the 29", but when you make it, you feel great.
I learned on a 29in with no previous experience with freewheeling. It was a challenge to put it mildly. Very rewarding however. My eventual exposure to a 20in freewheel was easier to mount and start. It was a brakeless contraption used by the San Luis Obispo riders and it scares me.
I am still amazed by your coasting. Inspiring for sure. Hope to one day coast half as well as you. Legend has it you, like Chuck Norris, can coast uphill by your willpower alone.
After a long time on fixed unis I am starting to learn to freewheel. What an adventure. Following Finn’s great tutorial.
So far managing short segments around the neighborhood and some very smooth gravel paths. Free mounts are working on a third of my attempts.
My question: on a fixed uni, I try to keep my weight more on the seat as much as possible on smooth surfaces, more on the pedals over rough terrain. Is that the same on freewheel, or do you change this compared to fixed uni?
Don’t forget the other great tutorials in the top post in this thread:
AJ has done some great tutorial videos on getting started without a brake:
Mounting, pedaling, and dismounting:
https://www.youtube.com/watch?v=xFU8EKBkA3g
Brake coasting is nice, but nothing beats the feeling of coasting without brakes. It’s worth every hour you have to put in!
To answer your question: For me the weight more on the pedals over rough terrain is also true in freewheel.
I was planning to build a new carbon wheel with the pipifax for muni after unicon22, but seeing this is making me doubt
. Maybe I should just build a mountain BC wheel with brake, has anyone tried that?
After both my Pipifax hubs have had failures, I would strongly advise against building muni wheels with such hubs 
Well, then the question is whether I should put wireless brakes on a BC wheel or have a normal brake with the cable hanging in the air (risking to break it in a fall)
@rogeratunicycledotcom might be able to share some pictures of such a thing here.
Have either been fixed?
Is it just that the sprag bearing goes over-centre (breaking it), or is there another failure that happens (failure of the key or keyway perhaps)?
The second one has not been fixed, yet. I have not had time to work on it. I believe it is just a bearing that failed, and that is what David from Qu-ax seems to think as well. I don’t have more details for you, though 
Nico is the god of the BC wheel and I don’t think he ever tried a brake. Terry (Unigeezer) considered it but I don’t think actually built it. I made my various peg unicycles and took them off road and to skate parks. In my opinion a peg unicycle is better than a BC wheel with a brake.
– Carl
I was went searching for your peg unicycle videos, but it seems like your youtube account has been deleted. Do you have your videos posted in any other platform? Why do you consider a peg unicycle better than a BC wheel with a brake?
I bought a bc wheel before winter and Im still building up the guts to learn it. Ive had some bad falls with a freewheel, and I fear I will end up on my butt a lot. Though it sounds a bit like cheating witha brake.
What is a peg unicycle?
If you only now how to ride with brake (freewheel, peg or BC) and you consider yourself as able to ride I guess it could count as cheating. For doing steep downhill I think we could consider having a brake as the standard, although I guess it would be good to specify that it is Brake Assisted BC wheeling (BABC) to avoid confusion.
I wouldn’t take a bc wheel on a steep downhill. Naturally a freewheel unicycle requires a brake, as it is meant to be used to ride many kilometres. Im hoping/expecting a bc wheel to be lighter to handle than a UW, though with a UW I have much more control.
Btw, this is my freewheel & bc wheel youtube playlist. I’ve put in it all the relevant videos I’ve found so far.
The peeps in the videos on the bc wheel go very fast downhill. I wonder how easy it is to bail. As soon as you take one foot off the other clashes to the ground.
Couldnt you find a video about learning to ride bc wheel. I want to learn this year.
I have a video I’d like to suggest you add to your playlist 
42 km/h is the highest speed I’ve reached while filming myself with a handheld camera. I reached 46 km/h on a mountain descent a few months ago, which is probably the highest speed I’ve ever reached on a unicycle. Over the past five years, my top speed (without a GPS glitch) was 44 km/h with my G36 during the “Loop the Lake” race at the last UNICON (there was a slight downhill section on the course).
Paradoxically, I feel much safer at those speeds on a freewheeling unicycle. I want to push myself further, but if something goes wrong, it could be dangerous.
