Hi
I am about to buy my first unicycle off unicycle.com and I was wondering if it would be easier for me to learn because I can ride long distances on my mountain bike no handed
Yes it will help. But the unicycle will still seem impossible at first, so expect that. 
Hi Leptiptidium and welcome to the forum!
I believe that riding your bike no handed, won’t make it a lot easier for you. With unicycle you have to keep the balance against 4 directions, and it feels completely different.
It’s funny but I noticed many times while bicycle riders passing me, they start riding no handed, as they were saying: “hey, see me I can do it also!” 
Good luck!
UVcycle
Thats a start. I just started two weeks ago and have a strong MTB background. I have found that my cycling strength has not transferred much to the unicycle. It is very difficult for me to relax and keep a lot of weight in the seat, but its getting easier every time I ride. Just get started and stick with it.
You are going to love addictive challenge.
Mark.
Unicycling would be easier than riding the trails around here no-handed on a bike. If you’re comparing to riding a bike on smooth pavement the uni will be harder by a good measure.
A unicycle will probably seem very impossible at first no matter what other things you do.
The left/right axis is the easy one. It is the front/back axis that is the tough one. However, if you can stand on your seat while riding without hands it will probably be an easy transition.
Just keep working at it and you will be able to unicycle. It is an great sport, but I don’t think riding with no hands has much to do with it. Enjoy it and don’t give up!
Or the skills will transfer easily if you can do this on a bike.
