I've been running the Juin Tech GT-P 4 piston hybrid calipers for about 4 years now.   I chose these because of great reviews, and that I could use regular STI brake shift levers on my gravel bike, and not have to pay out big $$$ for indexed hydraulic levers.
4 years later I look back, and have not really been happy with them overall.

1.  For general riding on paved roads and some gravel roads with limited descending they worked great.
2.  On long steep or technical descents I have had many problems with them.
     -  Calipers overheating, and the mineral oil expanding and locking the pads onto the rotors.
     -  Brake fade on long descents.
     -  Almost continuously having to adjust the knob on the caliber because if too loose, then the brake lever pulls too far, or if too tight, often drags the pads causing overheating.
     -  rapid pad wear. 
3.  In about 8K mikes, I have replaced pads 4 times.
4.  About 2 weeks ago, the front caliper was working, then all the sudden it no longer stopped me. No matter how hard I pulled on the brakes.  Swapped to another GT-P caliper.  Cleaned the one I took off, opened up the bleed ports, and had to add some mineral oil.   No signs of leaking oil anywhere on the caliper.  I am guessing that a bubble must have developed and kept the pistons from pushing on the pads to rotor.   This issue almost caused me to crash on a sharp left hand corner.  Thank goodness the rear was still working.

I migrated away from these hybrid Juin Tech hybrid calipers to full hydraulic on my 29er hardtail that is set up as a gravel grinder.  Once I put on full hydraulic brakes, I realized how poorly the Juin Tech really perform.   

I Plan to swap out the Juin Tech's for full hydraulic this winter on my Gravel bike. 
 
I have become addicted the the ZTTO Carbon "H" bars.  I already have them on 3 of my bikes.  Even though they have less of a drop than regular flared gravel bars or road drop bars, I find them to work really well and they allow you to run mtn. bike hydraulic brake levers and the Wheel Top EDS derailleur.

Agreed. I have Juin Tech GT-F 4 and don't think they're worth they money remotely, and ultimately got a new fully hydraulic groupset. Do note that I've a heavy guy (180lbs) living in a hilly area, so it may be fine for you depending on where you live/how much you weight etc. For anyone who gets told that they're as good as hydraulic: they're not even remotely close, unless you bleed your hydraulic groupset really really badly.