Steel has been used for making Handpans, Pantams, Sound Sculptures and Hang Drums for 20 years now (read more about it here) but stainless steel handpans are quite like new comers in the market. So to better understand the characteristics of an instrument made of Stainless Steel, the best way is to compare it with Nitraded Steel ones.
Note that lots of characteristics of a Handpan depends on many factors based on the techniques which are being utilized by different makers, but in general, Stainless Steel Handpans have longer sustain, wider and brighter timber/tone, Bigger Sound Range or Amplitude, more Dynamic Range and less ceramic sound comparing to Nitraded Steel Handpans. These properties specifically make the stainless steel material more proper for slow playing which is maily being used for meditative and sound healing applications.