I would have thought that although a scroll saw is a fairly safe machine you could easily start the machine by mistake while you fingers were not where they should be, such as just changing a blade or removing an offcut etc
I can't think of a time when a foot switch would have been useful, I can only think of the potential safety risk
Once you have switched on the saw, you have both hands free so can't see the advantage
OK whatknot, "each to his own" as I suggested above.
NOT trying to convince you (or anyone else), but I find that especially when I need to stop cutting momentarily when doing a really sharp turn - 90 degrees or more - it's very convenient to just momentarily lift my foot off the switch while still having both hands on the work piece - and still probably rotating the work piece a little while not actually cutting.
Perhaps I should add that my foot switch is a simple "On/Off" switch, not with any speed control, like it seems the official Hegner unit has.
But as an additional very much personal comment, my EX 21 has no NVR. I know (think?) it's a UK safety regulation, but I can't see any value whatever in having one. As you suggest, even if treated with only a modicum of respect, a Scroll Saw must be just about the "safest" machine in the shop? And I can't see how even the clumsiest of user could accidentally start the machine while, say, changing a blade. Not when the "actual" On/Off switch is positioned where it is on my machine anyway.
But in one respect you are of course quite right - the potential for me to accidentally plonk my foot on to the foot switch while changing the blade is quite high I suppose. Because in my set up (no NVR remember) the "actual" On/Off switch is bypassed by the foot switch. But it hasn't happened - so far anyway!
BUT, as said "horses for courses" and all that.