I ain't arguing GEP, I'm providing another input on what is a neutral situation. Landing is inherently more dangerous than teaching a couple of teenagers to swap seats... But which requires more training?
Making a tonne of metal move in such a way that it flies at high speed through the atmosphere, with our delicate fleshy bodies on board, is not the cleverest idea anybody had (evidently), but we made it risk acceptable.
Same applies here, and in fact the major reason we will hear people voicing their opinion that it isn't a good idea is psychological - it's not what people are used to, therefore they will condemn it.
The bottom line here is that nobody on this forum (presumably) was present during the briefing the instructor gave these two young guys. A good rule for 99% of activities on life is the old 'it's only as safe as you make it'. Two mobile, physically able teenagers, briefed very carefully on how to move through a one foot gap without sticking their leg backwards, under the scrutinizing eye of an experienced instructor, makes this whole deal a non-event...
... In my opinion, because we're allowed opinions aren't we GEP
edited to say - For the record, I haven't, and probably will never do this, but my reasons are more along the lines of above posters with regard to training quality/issues. My thoughts above are on the safety aspects only.