Are they any good?

Have heard good and bad about tube buffers.Do they really work and if so which do you suggest?
They absolutely do work.

They can help change the flavor of the sound. The exact flavor change will vary case by case Whether or not that change is good or not is somewhat guided by specifications but in the end mostly a judgement call.

The nice thing is that adding one is easily reversible,you can easily use a tube buffer or not with existing gear without having to change the gear.

The aspects of sound most likely to be noticed as different will be dynamics, including transients, noise levels, and frequency response.

Note that the tube buffer is not likely to add detail that is not already there, though the difference in sound might result in drawing attention to whats playing differently. SOme things may be emphasized others deemphasized, but no component can add what is not there, although it is possible some things might be filtered or transformed in a positive (or negative) way.
good if compression is needed(indeed sometimes).
I have tried a couple of tube buffers after a cd player. Total waste of money. If you have a ss preamp and want to add tube sound get a tube preamp, not a buffer. My opinion
Have a NAD 3020 SERIES 20 and would like to keep my phono stage.Was thinking, more for using with a cd player.
My mhdt Paradisea DAC has a built in output tube buffer. Tube rolling is very effective for tweaking the sound. The stock GE tube it came with adds a lot of tube flavor, ie softer dynamics and some frequency rolloff at both ends. Nice sometimes but colored overall and not the best for all music. The alternate Tung Sol tube I use makes the sound very close to my other DAC, a mhdt Constantine SS DAC with no tube buffer. So the effects of a tube buffer can be quite pronounced. The ability to tweak via tube rolling is a nice benefit.
Back in the 90s I had a Sony receiver that offered effects to tailor the sound with settings such as Hall, Stadium, Jazz Club and a few others. They could've had a setting for tube; they missed the boat there.
It seems strange to me to stick another component in the system chain with the purpose of inducing "noise." I own a few different amps, one of them is a tube amp. In fact, I just put the tube amp back in service a couple days ago.
"It seems strange to me to stick another component in the system chain with the purpose of inducing "noise."

You do it in order to change the sound. Everything in a signal path does that to some extent. This is just another way to do it without replacing anything. Its a choose your distortions kind of thing more than noise.

I would agree that you only add things into the signal path for a good reason. Whether this is a good one or not is really a judgement call and like most things involving home audio sound quality will vary greatly case by case.
I agree with Arh, I would not spend on a buffer. If you want tube sound from a component, buy it with tubes. A buffer will only add to your cable issue of another post. The fact that you are using the NAD 3020 answers part of my question on that post. I will get back to you there. Enjoy!