You are able to open multiple oldschool clients:)
Just make sure the first one is hooked prior to opening a second one.
What specs do you have on your laptop btw? Mine are quite high but I can't even run two mirrors
Extreme AIO Hunter has been running fine for the past hour with no lags.
I'm also running Perfect Strongold on my other account though which is experiencing insane lags (on a high spec laptop) and keeps breaking after no time at all.
The lag was from mirror. I'm still getting quite a bit of lag after MGI's fix so report it in the bug section of mirror client and let MGI know what the issue is