The engine use old technics, their implementation of BD and avira is useless, the "essential" version have slow update ring, and non "essential" is bloated.
Bloated - agree in parts. A typical Internet Security Suite with the bonus cleaning tools (compare it to Avast, Bitdefender, Kaspersky and other suites).
It replaced additional tools like CCleaner for me...
Qihoo's signatures a pretty strong to my experiene. Have activated both BD + Avira, as it does not affect memory noticeable at my machines, and offers offline protection (seldom offline though). Cannot tell whether the engine is outdated.
Used Essentials for more than one year, but replaced it now with the "bloated" 360 TS, because of the faster update rig (they fixed problems of the old version within a week, so did they with some German translations).
Compared to KIS, BD IS and Avast Pro it really does a great job for me and is free. Most important point for me is that they react to new Windows Versions very fast, concerning compatibility. Had a massive issue with KIS 2015 there... BD IS was replaced two years ago, cannot tell about that (very bloated too). Avast Pro was quite ressource hungry on high sec settings, so I didn't renew the licence

Never had contact to other customer services but Qihoo (KIS + BD had their issues, but I used Internet to fix that), but I think, they do a great job (regarding SUD and technical issues) and reply fast. That might be the point I prefer personal contact.