Hi and welcome to the forum,
I've got the air ranger (so no electronics) and I'm happy with it, I've also owned a Mk 3 and the battery pack did eventually fail - probably my fault for not charging correctly but is a simple fix.
A few years ago a lot of people who shot HFT owned a Mk 3 or Mk 4 and most shooters seemed happy with Daystates, however in the past couple of years though they have lost popularity for what ever reason . I personally like Daystate and have had good customer support in the past.
They are at the expensive end of the spectrum of guns and if you have a S510 already you may not see a vast difference apart from the trigger. If you want a Daystate I'd go for the Ranger or Huntsman as they don't have electronic components and so easier to fix/service and require less maintenance.
Weihrauch HW97 .177, Weihrauch HW80 .22, Weihrauch HW77 .22