Been driving this car for 1yr 3mths now, mileage 29k, daily drive to work. Executive variant.
i. 3 cylinder engine - no issue. so far so good. bising? inside car not bising at all. vibrate? NO!
ii. support & service - depends on where you go. 4 SCs i went, 3 were good, 1 SC (Proton Regal Motors PJ) SA & pomen super rude.
iii. service cost - can refer the cost on Proton app, just follow the app, if they want to add on service/item, just say NO!
iv mechanical issues - mine no problem. apart from battery cap unta kaput less than a year, but I cant claim warranty bcs mileage more than 20k. warranty cover 1 year, 20k mileage only now my car aircond issue. not cold, only blower. i suspect gas bocor. this wednesday got appointment, see what's the problem.
v. spare part price - not sure

since this is my 1st car, so i cant judge other cars apart from my dad's kancil & my sister's saga.
all in all, nice car to drive. paling laju i drive 160km/h je, no vibration, & stable.
but sometimes when want to overtake, can feel a bit turbo lag.