Okay, so I've read many a "horror story" on the FCD myself... but personally never had a single issue in over 17 years with mine in numerous boost/turbo combinations, but here's the CONDITIONAL statement I will qualify a response with:
IF the FCD is used AS designed by HKS and in perfect compliance with their literature and integration of HKS components (electronic), I believe it to be a very reliable device BASED on MY personal experience.
Deviate from the above, and all bets are off.
(For the record, my FCD has ALWAYS been in use, WITH the PFC F-con and my boost controller has been the early EVC unit. I have run 15psi peaks on stock CT-20, 15psi on H3 Hybrid CT-20 for more power, up to 17psi on BOSS Sr. turbo and now 15~18psi on T04z without any issues.)
Good luck!
Note: I highly recommend careful review of ALL HKS installation literature and Manuals and diagrams as part of this process.
PS: A GOOD AFR (like NGK Powerdex) is a MUST in ANY modified setup, and I further recommend an EGT in conjunction with it for good feedback to prevent "meltdown syndrome"...
-crisp