Reliability ZERO.
App full of neat and usefull functions. Works fast.

But evry day something happens that kills my groups.

for ex: If you close the window with alle the groups in it and restore it afterwards, tha taps arent in the group anymore. if you change to the saved group its full of empty tabs. some of the tabs might still work but most of them are empty.
all the groups are worthless because they are destroyed, without backup either way from firefox recovery session exprted tab backup you're screwed.
After closing and recovering the window you need to delete all the corrupted groups and save the currents window into a new group. you cant create tabs that arent in a group after you have already more than 1 group active.

Once All my groups just disappeared without warning. wtf?
and so on. full of bugs makes it unrealiable. but its potential is great.