Which is more reliable, Panel Optimizers versus Microinverters

[solardreamer]

With string inverters, the installer needs to inventory several inverter models to match up with different size strings. With microinverters, they just need to stock one model and size.

This makes more sense. There are also multiple models and sizes for microinverters but it's much less expensive to stock them.

[J.P.M.]

I have heard that with some installers, actually finding the roof trusses are optional

I'd like to support that statement.
I've watched most of the installs in my HOA, ~ 175 and counting. It's always been fun and an eye opener to watch installers/workers setting posts or support fixtures for panels into roofs.
The usual method around here and usually quite easily observable from the ground that I've observed from the "Larry with a ladder" type installers, and others for that matter, is that a hole will be drilled in the approximate or guessed location of a rafter. If missed, another hole is drilled an inch or so to one side or another. The process usually continues until the rafter is found. The holes remain and may/may not be sealed. Installers don't seem to care if their help from the big box parking lot temp. employment agency know about hitting a rafter, or much of anything else for that matter.
Reputable installers do a lot better but usually the supervision is less than necessary to prevent such B.S. shenanigans.
Thank goodness there is not much wind around here. Factors of safety exist for a reason, but the day a strong wind storm shows up around here may well be a day of reconning that will overcome such conservative methods.

[nerdralph]

This makes more sense. There are also multiple models and sizes for microinverters but it's much less expensive to stock them.

It's much less expensive not to stock either. I keep a spare string inverter on hand. Other than general supplies like MC4 connectors, wire, and some panel clamps, I don't keep inventory. If I need 20 panels and a 7.6 kW inverter for a job, I order them from my distributor and send a guy with a trailer to pick it up and bring it to the customer site. With prices falling like they have been over the past year, keeping any inventory can be quite expensive. Both SolarEdge and Enphase have had terrible quarterly results due to high inventory and falling prices.