What are the most under-appreciated products?

Sar Labs or Scientific Audio Research Lab...
A one man operation and his flagship power amp ..the Mos 400
is produced at the rate of two a month.
Great sound at half the price.
No, I'm not related, just a satisfied customer.

Herbies Hal-O tube dampers. I was amazed at how they increased the 3 D spacial characteristics, plus tighter and deeper bass. It was like getting an amp upgrade.

Ever since I owned a pair of Sequerra Pyramid MET-7 speakers in the mid-1980's, I've had a special appreciation for them. While they got some positive press from The Absolute Sound some 20 years ago, they've pretty much dropped off the audiophile radar screen. Dick Sequerra continues to modify and improve this speaker, and even at its current price of around $1200 per pair, they offer a lot of performance: imaging, midrange accuracy, and musicality.

Hey TWL, does your Emission Labs tube recommendation apply to 6DJ8 and 12AX7? Or how about EL84? Thanks.

Now this is getting interesting. ASR, Sehring, Scientific Audio Research Lab. Those stumped me!