Not universally true.
The problem is “balanced” is a very vague term used by manufacturers. Is the output truly balanced or just using a balanced output jack? Yes you can get this adapter as you mentioned, and you won’t damage the amp most likely. You probably are safer with transformer coupled adapters by the way. But, there is no guarantee that this arrangement will sound good or actually work well. Not blowing up amp and working well two different situations.
My point is I wouldn’t recommend using this adapter (or adapters in general of this nature) from a true balanced out to SE device unless your confident the combo is safe and sounds good. And where this ifi adapter may be good, others may not be so well designed. I would in general suggest just don’t recommend it. Except for headphones like Grados, just buy a balanced HP cable and get the full balanced goodness.
I can’t think of many if any non pro devices that are balanced only. Only Geshelli comes to mind. Most of the time I read people thinking the balanced out is somehow better than the SE on the device in question and, instead of getting a balanced cable for their HP, they do the adapter instead.
So I stand behind my statement and recommendations. IMHO and YMMV of course.
I believe with 4.4mm it is all but universally true even with fully balanced amps, there may be some oddball device of course.
There are some amps that don't use the ground of the 4.4mm headphone output so in that case the adapter simply wouldn't work, you would only have the two positives connected and nothing else so no circuit and no sound but no harm.
With a normal balanced amplifier that has a functioning ground and the positive and negative per channel the adapter simply makes a single ended circuit leaving the negatives unconnected so no short and no risk. That is what is happening inside most balanced devices with a 3.5mm jack, they don't usually have a dedicated 3.5mm amplifier, they use the positive from each channel and a common ground just like the adapter does. The adapter will sound exactly the same as the 3.5mm output.
It isn't rocket science and there isn't anything odd going on it is just a basic circuit. I checked this stuff with a very qualified chap via private message and he confirmed my assumption on the circuit created and the 3.5mm single ended output from most balanced devices.
Also iFi are unlikely to make adapters that are fundamentally dangerous, their website explains how they work.
Of course there might be bogus adapters from dodgy sources but that doesn't alter the basic premise that it can be done.
Whether there is any need or value is of course another mater and in principle I agree the less adapting the better, if only for the sake of technical niceties.
Reversing the concept and using the adapter on an input as in the case above that started the conversation is obviously technically different. In that case the adapter will connect the 4.4mm negative input of the amplifier to the ground of the 3.5mm source device but that is the input side so essentially all that is happening is the negative side of the amplifier doesn't receive the negative signal, the voltage isn't being received by the amplifier and there is no short That isn't dangerous but as we both stated isn't going to make proper use of the balanced architecture anyway so it a pointless exercise.
This is all just technically interesting, to me at least, and has some limited application but for the most part isn't of great practical application although I do occasionally use the concept in one set up and have tried it with many others with no ill effects and perfectly normal sound quality.
I get your point but I believe that technically it is very rarely true and I just think it is best that folks understand what is technically accurate, there are lot of comments about blowing things up which, for the most part, are based on a lack of understanding of the circuitry.