I prefer the sound of T51 to Studio V. At least that is on my iem but I can't say for sure regarding dynamic iems. The output impedance of the Studio V might be very high and cause all sort of problems to armature iems. Hisound chose a cheap way to increase the impedance of the iem through the use of impedance cable which will certainly degrade the SQ and reduces the dynamics.
The T51 is a better designed device overall specially targeted at audio but failed at their QC as well as product usability.
Each has their own critical flaws. Can't really say which is better.