For all my experiments the Pi is isolated via either transistors or opto-isolators. So, there's no problem with the external circuitry loading down the power supply for the Pi. I've used various Pi modules over the last several years.

There are definitely stability issues with each model. The most annoying problem I've encountered is finicky networking. A common symptom is showing a connection as active, but the unit is inaccessible via other network hosts. I've answered several of these questions myself on StackExchange.

Unfortunately, StackExchange doesn't hand out STEEM for upvotes.... Perhaps someone will re-create a technical Q/A through STEEM Engine. Then I could enjoy some financial rewards instead of a few 1000 "points" and a good feeling.

In my experience, the Pi is not suitable as a critical component in a project's system architecture... it's best not to rely on it to be fully functional 24/7.