The precision is potentially better in that they have much finer threads. The required force to turn them would be lower because of mechanical advantage. The downsides are speed and durability. The angle of the bearing surface is not as strong and the smaller, and non-hardened thread will wear faster. It also cannot handle the forces as well (acme threads are pretty beefy.) Everything in life is a trade off.
As far as the bearings, any time you have a hardened steel rolling or rubbing against something as malleable as AL, you can have problems but overall, I wouldn't be worried about it on a hobby machine. All parts will eventually wear and need to be replaced. Just keep an eye on it and if it becomes too much of a problem, then think about replacing or upgrading.