I'm just a hobbyist in mugs, I have similar and I've done ok with one but only done 36 mugs, all depends if your doing it as business or hobby I think, I don't have much experience but I thought I would reply to question.
I use something similar and recently bought a spare standard heat element/pad. I think if I need a backup I would try for an almost identical press to the one I have because I already discovered my old press and the one similar to your picture work completely differently on times and pressures.
I actually prefer the cheap ebay press to the more expensive original press, but I wasted some mugs learning the difference.
I have back up machines but only because I have replaced machines along the years. If I was starting out now I would not purchase a back up, but instead leave the money in my business account. Should the primary machine malfunction I can always purchase a new machine which would be with me the following day, but then I would never purchase a machine from Ebay, I know there are good as well as bad suppliers on there, but its too much of a risk to my business personally speaking.
Yeah, we don't have backup presses, we just have presses that get used, if one goes down, we still have the other presses that we use, just means we make a few less mugs per hour.