Older or Newer One touch unit?

hi there, ive been using a old one touch unit, think about the 80’s modle, it is pink and tan colour, with a horrible beeping noise lol ive now also purchased a newer one touch, its green and white, with no beeping sound or lights present, with trademark 1997 on the box.

My question is, is one of these better than the other?? my older one seems to beep for about 40 seconds, but the newer green one says one leave it in for 15 seconds… does that mean its stronger in current? or does it simply mean the times have been shortened because people have gotten scarring etc? any help would be greatly appreciated, im currently using both each day to try and get the best and fastest results. thanks, ez