Are there any decent ones that offer feedback detection?
JP
Your ears are the detectors, and they are far better than any device at determining when something isn't right. Whether or not you're able to correct the problem is another matter entirely, and success in that comes from experience. There is no box, no device, that will "save" you from either system setup stupidity, asking for more gain than can be had, or "talent" that can't keep the mic from pointing directly into the PA or monitors.
Make some feedback, burn up some HF drivers. Learn how to replace the diaphragms... and consider this part of your tuition in Ye Olde Skool of Audioism™. You'll get better, faster, when it's expensive. Dr. Freud said so.
Have fun, good luck.
Tim Mc