An SR type latch, made from two inverters fed back into each other... can very easily be made with two npn transistors, and is much more stable and predictable then a PUT latch. Its been my experience breadboard-ing a PUT, that it can sometimes start up high, and then maybe low the next, and sometimes won't latch on permanently, (might toggle back after a few minutes), and it can be really sensitive, even with biasing resistors... this nice double inverter latch can really help eliminate those problems, and it's very simple, still requiring very few components; I've also breadboarded it using transistors, and it works flawlessly
