To answer the original questions, there can be reliably and potentially safety issues with OTL amplifiers, especially early designs. The best implementation I've seen are the Berning ZOTL amps. They are safe, and reliable. Most won't require retubing for years, or decades. They have autobias, and protection circuits, plus very low output impedance, making them very versatile in matching them to a wide variety of speakers.
As well as the models available on his website, or licensed by LTA, David has a collection of small, lower power models available he doesn't promote on the website that includes 300b SET and PP, 6b4 SET and PP, 845 SET, etc. All the models I've heard (and owned) sound outstanding.