i can confirm that even on nexus 5 ubunti is so far to be optimized..but his ui is not bad,but is nice, organized in scopes, even if i prefer much more sailfish os' one...many apps are only local version of site.. multitasking is not absolutely necessary but is beautiful and could be useful for example when i open some webpage i make other things when i am waiting it loads.

i really prefer behaviour of sailfish jolla wich,even if not open source completely, about core and other than ui components truly give an hand to oss. neither jolla neither canonical seem to be perfect under this field, however,for different matters