Mechanical contactors do have a limited lifespan compared to solid state switches, but have lower on-resistance than SCRs and IGBTs (cheap solid state power switching) or all but the best FET technology (more expensive solid-state switching). I would assume the contactors are a replaceable part in this unit, at any rate(?). If it's incurring only 5-6 cycles an hour (which it sounds like) don't sweat it, but if it's ever finds a mode where it's doing dozens per hour it's time to do something about it. If there is a way to adjust the hysteresis in the controls to increase the minimum on-time it's the right thing to do. You might buy a little bit out of increasing the flow rate too, or not- it depends on how internal controls of the boiler determine when to turn on & off.
With electric boilers the efficiency is going to be the same at either temp, independent of the number of cycles it's running.
Even though the heat delivery is via air, heating with mini-splits has very little in common with ducted air systems from a noise & comfort point of view! Being fully modulating systems with variable blower speeds you don't get the undershoot/overshoot hysteresis in traditional bang/bang on/off single stage hot air furnaces or even 2 stage furnaces- room temps are very stable, with continuously sensed and adjusted input & output air temperature control. In the outdoor unit scroll compressors, variable refrigerant volume, and fully variable speed DC ECM-drive fan motors takes all the rattle & hum out of those too, making them ghostly-quiet compared to their traditional single speed reciprocating compressor AC-drive fan ancestors! The interior head of the -FE18s are significantly quieter than most refrigerators when the blower is at low or mid-speed, but it can get pretty gusty sitting in front of the head when maxed out (but still nothing like the rattle & roar of a 1-ton window AC unit.) Heating with mini-splits is nowhere near as cushy as radiant floors, but it's still a huge upgrade in comfort from heating/cooling with old-school ducted air systems.