Both my ACGs live in the Mono Sleeve, and of all the Mono cases it's my favourite model... and this from someone who has owned them all!
It's well padded, the pocket actually expands to be pretty big (I put my Tecamp Puma, a speaker cable, instrument lead, power lead, strap, tuner, patch lead and iPad in mine for rehearsal last night), and like all Mono stuff it's really well made. I have had no experience of the splitting Ambient mentions.
There are three things I'd change if I could though:
i) the buckle system works, but is a bit naff
ii) I'd prefer the bottom of the outside of the bag to be lined with the heavy duty rubber used on the Mono backpack range
iii) I'd swap the orientation of the handle to the other side, to make it a more natural carry for right-handed folk
All round, an excellent bag though.