For me,
Driving position, derated engine doesn't work well with the I-shift,
The nearside mirror is unnecessarily bulky, low hanging and sticks out too far - have to be extra wary of this at bus stops in regards to people and places where you're tight against walls or foliage.
See -
View attachment 85307
When battery charge is low they're very jerky in low gears, in regen mode / low charge they're jerky pulling away and difficult to drive smoothly and struggle climbing hills often trying to use almost every gear. Gear changes can be slow so if you've pulled out safely on a roundabout or junction traffic quickly catches up to you so you have to bear this in mind when making decisions to pull out.
There's certain situations (e.g turning left off Hailesland Road onto Murrayburn Road) where they'll try to pull off on electric power but the motors aren't powerful enough so they'll just stop, engage gear and try again in diesel. Occasionally the 13 plates just stall in that situation.
General build quality isn't very good, I believe they were made in Poland - I've driven Swedish and Polish built Scania OmniCitys before and the difference was night and day in regards to build quality. The cab area in particular is quite rattly on a 7900.
Capacity is/was an issue before covid.
Don't know why the B5LHs are so different to drive, rarely have any of the above issues when I've driven those so can only really put it down to the single deck chassis being derated in terms of engine power and presumably the motors. The 14/64 plates with the more powerful euro 6 engine are better but still suffer with the same issues.
Obviously they're maintained to the highest standards so there's no issues there - but in my opinion they're just a flawed design.
Probably why there's so few of them in the UK but I don't think there was any real full diesel alternative at the time for single decks?
That's my Top Gear review of a 7900 - brought to you from inside a 7900

. Wouldn't know much from the engineering perspective of them but the impression I get is they're not well liked either.