I tried out a Tone Gard on my Flatiron F-5 last night, with mixed results.
The gard did make a big difference. Gave it a bigger, fuller sound with a little more sustain.
I liked it somewhat.
But when I took it off, I liked the old tone better.
I decided it let a lot more low-mids reverb in the instrument.
Without it, the back muffling made the highs stand out more and made the instrument sound more balanced.
In other words, this instrument's most pure voice may not be its best voice for my tastes.
But I'll keep experimenting with it.
On the other hand, I next put it on my 1917 Gibson A-1.
The change wasn't as dramatic.
But it simply made the good parts of the sound better and
Interesting piece of equipment, though, and I'm glad someone invented it. I think it will help a lot of instruments.