Stako's are safe to fill to 4,500, but because the safety margin is less that a standard bottle I decline to buy one. I trust myself, but I lend my gear out sometimes to total strangers, if their need is great. I want to know, that if I go to a fill station I have never been to before and it is capable of flash fills, I have the chance to slow the rate down before it goes bang. I would take the extra margin of safety over the weight advantage, but thats me.
Stako's were developed with tournament players in mind, buy one in confidence that if is a safe bottle, but use it only in official tournament events and training where you know who is providing the air. Never take one to a walk on site and note they do not have to advertise that the do not fill stako's, because it is a private site and they already have the right to refuse you admission and if they are not happy with you or your equipment, they can prevent you playing.