I'd agree that tube equipment is not the black and white situation some perceive. I've had many pieces over the years, building kits from scratch back in the late 60s and 70s and rebuilding quite a few amps the past 10 years or so as a hobby.

The odds of a problem with a tube amp are a bit higher than with solid state equipment. I had an output tube failure take out a 100 ohm resistor about a year ago. That's an incredibly cheap fix if you can do it yourself and a more expensive hassle if you have to take it to the shop, but it still cost me another $160 for a new quad of output tubes.

If a person just wants to test the waters with the lowest risk possible, a preamp is a good choice. Preamp tubes last a long time and rarely damage things when they go bad - you just end up with extra noise or no signal passing until you pop the new ones in.

Equipment using the smaller wattage outputs (EL84, etc.) also tend to be more forgiving than an amp with KT88s or 6550s. It also doesn't hurt to see what people have to say about the reliability of various brands. Some are more notorious than others.