I just got the Jcat Optimo Nano and it is every bit as good as I expected it to be (knowing that it is build upon state-of-the-art LT3045 voltage regulators).
Depending on the card you are using, the difference can be from jaw-droppingly-good to slight, but still worthwile.
If you were running the Jcat Femto USB card without a quality external PSU (using dirty mobo power via Molex connector) the difference is literally jaw dropping. Sound staging, fine details, body of the instruments, palpability - we are talking about a completely different league. Switch back to dirty MoBo power and the Jcat Femto USB card sounds broken.
Compared to quality, ultra low noise external PSUs I had on hand - the (discontinued) Jcat / Bacoon 02 battery PSU and Teddy Pardo PSU - Jcat Optimo Nano inline voltege regulator sounds more transparent with more fine details. Both battery PSU and Teddy Pardo had more mellow perspective, lacking a bit of air.
The difference on the more expensive, €800 Jcat XE USB card, which itself has 4 LT3045 voltage regulators (same as Optimo Nano) is much smaller, maybe 5-10%, but still worthwile.
Same on €1900 Pink Faun Ultra OCXO USB card - Optimo Nano pushed it from the hi-end to trully spectacular.
This is the best sound I have heard from my setup in 10+ years building audio servers.
Needless to say - I'm keeping the Optimo Nano to power my Pink Faun Ultra OCXO USB card.
BTW - seeing a heat sink on the Optimo Nano, I was worried it may get very hot under a high load. Pink Faun is very power hungry due to the OCXO used (which consumes a lot of power to keep the XO's oven warm) - it needs 1,1A during heating up for around 40 seconds and 700mA @ idle - but Optimo Nano heatsink never got warm to touch. A good sign.
Each LT3045 regulator is 500mA rated, Optimo Nano uses 4 in paralell, so the 2A rating given by Jcat sounds about right.