Electronic engine controls: good or bad?

Retrofitting electronic controls on non-electronic engines is a pet peeve of mine, for two reasons.

First, they don't fully replace the mechanical controls, neither for the engine governor nor for the gearbox. They rather introduce an additional layer of complexity - i.e. other malfunction possibilities - to a system that remains mechanical. In other words, instead of moving levers at the helm which directly push/pull other levers on the engines and gearboxes, you move levers that send electronic signals to a blackbox, which in turn controls some actuators, which eventually move the very same governor and gearbox levers as before. And if that sounds complicated, well, it's because it is.
Secondly, I like better separate levers for throttle and gearbox, but this is of course a personal preference.

Bottom line, in your boots I would stick to the hynautic stuff, but I'd have them serviced by someone very familiar with them.
And I would also save any money on the synchronizer, by simply getting rid of it.
I'm well aware that analogue tachos aren't accurate enough for engines sync, but the beauty of twin diesels is that you can do that just by ear - it's simply a matter of knowing what to listen for.
If you mind any harmonic noise, and fine tune the throttles till it disappears, you'll run them as aligned as with the most sophisticated synchronizer.

All that said, Glendinning controls are pretty solid, and while my personal preference would be for Kobelt, if you decide to downgrade to electronic controls, there's nothing wrong with Glendinning.
Besides, if your mechanic is already familiar with them, it wouldn't be a good idea to twist his arm into anything else anyway.

I m not a big fan of electronic controls. Too many things that can go wrong at the wrong moment.

On medium size boats, say up to 60/65, You can’t beat cable controls even with dual stations. Simple and you get plenty of warnings if something starts getting loose... they just don’t feel right.

On boats with a second station, they still work fine.

I couldn't agree more.
But if the hynautic controls the OP mentioned are the ones I have in mind, they are a very different animal vs. the Teleflex/Morse cable controls.
Hydraulically operated, with an air expansion tank in the e/room and actuators pushing/pulling the governor and gearbox levers.
They used to be a sort of "higher end" choice, back in the days of mechanical engines, compared to mechanical cables.
And they were indeed very solid and well built. As I recall, they also allowed a third station, as opposed to cables which can only handle two.
That said, on a '95 boat, it's not surprising that they should be serviced/tuned...
They are nowhere near as simple as cable controls, though.
Hence my previous suggestion to look for someone who already knows them well.

Cruising at 25 kts, I suppose with rudders centered, then one prop suddenly slows to idle speed (but still spinning), and the boat hooks?!?
I'd be curious to hear what boat she was, if you don't mind me asking.

Nope, that's also included as standard in Kobelt actuators.
If you look at this webpage, the actuator levers with red and black balls on top are the ones that can directly push/pull the mechanical cables connected to the governor and gearbox.
In case of any electronic fault, they remain 100% functional.

BTW, normally those actuators are meant to be installed inside the e/r, wherever suitable for keeping the mechanical cable length as short as possible.
But I've also seen a boat where they were installed inside a cockpit locker, thus allowing not only the emergency usage from a position more convenient than inside the e/r, but also the usage for maneuvering.

I used to run a 70 footer with Morse electronic controls. There was a back up cable control on the aft deck but to enable it you had to into the ER and flip a lever on the servos. Trouble is that they were mounted outboard of the engines and impossible to reach when engines were hot. Brilliant install.

over the years I had one series of intermittent failures on the port engine, first one happening when docking up at fairhaven shipyard then while transiting woods hole is heavy fog. On both cases had to finish on the stbd engine.

while the Morse had a diagnostic LED, it translated in unknown failure... I eventually traced to problem to the gear control cable between the servo and the gear, it had been moved by a mechanic during service and had too much friction triggering a failure

had it been a mechanical cable All the way, I would have felt the added resistance right away.