Lol, as the owner of a recumbent tadpole. They vary in stability; mine (a mid 2000s vintage Catrike Speed) is super low to the ground and pretty hard to tip. But the inside wheel lifting up in hard cornering is part of why they are fun. Its a different experience than riding a bike. You
feel the cornering forces.

But if you get too overconfident you can definitely flip them.
You are very right on visibility. A flag helps others see you, but you really have to be mindful around parked cars and such. And a mirror is basically a necessity; you can't really shoulder check whats behind you like a standard bike.
I don't ride mine all that much, and when I do its mainly on the quiet town side streets or the local MUP. Its a great MUP cruiser, the one near me is oriented axially to prevailing winds, so you sometimes get wicked headwinds that can make riding the normal bikes pretty miserable. When you're 24" off the ground the wind is almost a non issue.