Hi Glyn, my parents have a Vent Axia Sentinel Kinetic Plus B (from before I worked in MVHR) and it does have some reasonable components (good fans and good heat exchanger) some of the other parts are a bit cheap and prone to problems.
The summer bypass is a plastic part with lots of flaps that seams a bit flimsy and leaky, and there is a thermal actuator that opens and closes them. This has a very thin plastic pin (only a few mm) to connect to the flaps and in my parents unit this snapped leaving the summer bypass partly open through winter. Because of the lack of monitoring in the unit there was no error to warn this had happened.
Also the bypass air route is to the front and back of the exchanger and is separated from the opposite air stream with a bit of foam stuck to the side of the exchanger. This would be ok except that there is nothing stopping you pushing the exchanger in too much allowing air to leak around it and no guide to show when it is pushed in the right amount. It also relies on the front and back covers that are a bit bendy.
Also the plastic tabs that the front cover is screwed into break really easily and how well attached the front is is vital to the unit’s airtightness.
My parents’ exhaust fan died after 4 years, didn’t seem to be the bearings, as can happen in any unit due to the extracted moisture, but rather the electronics so has had to be replaced after eventually getting someone who could supply one.
It’s worth making sure the unit you choose is robust and has good aftersales support even if it doesn’t have lots of bells and whistles. Most important is to make sure, at your normal airflow rate and duct systems’ static pressure, it is quiet enough and has a low power consumption and I would say to make sure it has a summer bypass. If your house is very airtight or if outside air temperatures drop below freezing for prolonged periods a frost protection preheater or some other strategy that doesn’t involve reducing the incoming air is important.
But most important of all is the duct layout to make sure static pressure is low, components are ones that will hold up, enough sound attenuation is used, intake and exhaust well insulated (if inside the house), any ducts in lofts are under the insulation, intake and exhaust grille locations don’t have issues etc.
The only way to know what the static pressure will be and the sound levels at valves in advance is to do a design where these are modelled. Otherwise you end up doing what a lot of MVHR installers do in slinging it in and hoping that the required airflow levels can be achieved with the system being inaudible. If it can’t they either turn down the airflows to make it quiet or leave it at the right airflows but noisy so it gets turned off and now you have no ventilation.
The system then also needs to be well installed but having watched your heat pump installs I don’t think that will be an issue.