I like how Glyphs remembers tabs and their content. It would also be helpful if it could remember in which writing direction a tab has been set; at the moment it seems to always revert back to LTR.
On a similar line, switching to RTL preview seems to enable Arabic shaping by default – I don’t have to manually activate the init, medi and fina features. If that is correct, it would be consistent and make sense to also have rlig activated by default.