The muscle issue is the dimples yes, they can be very bad, or they might not happen at all. Most people end up with some scarring. Later on ill find a pic of when i had them, i dont have many pics tbh but ill see.
Personally if holding/gluing some balls to your face doesnt convince you that you will like them then getting one side done imo is a mistake because say the result is, you dont like it, and remove it(you wont really be able to tell until its downsized etc) you might be left with a dimple on one side. Basically I'd say either get both or get neither really. Sounds a bit patronising I know, but Im sure you would prefer to be left with symetrical dimples than one side if you didnt like them?
I havent but there are some pics in their portfolio of ones they have done.