I know nothing about the Argentine snaffle but I personally don't care for anything with the combination of shanks and a broken mouthpiece. I start all of my younsters in a loose ring snaffle and then when I feel they are ready (neck rein pretty well and are well behaved), I move them up to a swivel shank curb with a solid mouth.
This is the same type that I use on my finished horses.
The swivel shanks allow one handed correction when necessary and there is enough of a port for tongue relief but not enough to interfere with the roof of the mouth (in most horses).
On another note, any bit can be mild or harsh depending on the hands of the rider. All bits have the potential to inflict pain if used improperly (even simple snaffles). However, there are many people who absolutely love those bits that all others say are "incredibly harsh" because they use them softly and have good results. I have known people that had wonderful results in a tom thumb, spade, cathedral, etc. However, I have also seen the disasterous aftermath of those same bits in other hands.