I have mini-humbuckers in my 1974 SG and I do like them quite a bit, but they are their own animal.
But, you’re right; they can be susceptible to squealing at high volumes. In addition to the fact that they often aren’t potted, the bobbins aren’t even affixed with screws to the baseplate, as they are with full-size humbuckers. The bobbins are held in place by the cover.
This does let the pickup behave more microphonically. At lower volumes it lends to a lively sound, which is one of the things those who like mini-hums most like about them. At higher volumes, you can get squealing. However, I’ve found them to behave okay with moderate gain. I did have one of the pickups get too microphonic on my ‘74 SG. I potted it and fixed the issue. I never had any squealing issues with it after that, but I admit that it took away some of the liveliness of the pickup; sometimes I wish I wouldn’t have done that. But, if you use in-ear monitors instead of a wedge and run your speaker in an iso-cab, or use a processor, you avoid the problem altogether.