I’m slightly baffled by the issue some people had with this, especially those of us chestically blessed.
I’m a 36G/34GG, and like to compare myself to Gimli but without the beard (and I’m a bit taller). I didn’t have a problem fitting the pack on my back, the cross-body strap was looped under my breast and I ran a half marathon and 5k in it with no issues. I also used it as a hip bag for travelling.
Had no rubbing issues on my neck (which I thought might happen but thankfully didn’t) was able to fit a 500ml soft flask, baseball cap, gloves, a 300ml water bottle, and 50ml bottle of water I picked up along the way. At the end, I crammed it with more stuff to see how much I could get away with (managed to get in two oat bars 😀)
If I had looped the cross-body strap under my armpit as I saw in the ad, I probably would’ve strangled myself and not gotten very far. Whilst running (probably because I’m not a speedster), I was able to unhook it, get water out, put it back in and manoeuvre it around to my back and hook up the strap without any problems. The cross-body front strap made it under my boob with enough left over that I could cinch the bag down or loosen it.
Would I recommend it? Yes, I wanted something that could be used instead of a hydration pack and it ticked all of the boxes for me, especially in terms of comfort and capacity. I honestly can’t complain about the price tag as I bought it, and it was the only item I could find that fitted my requirements.