Couple of points
Apparently you are reading a bit more into what I said than I believe was there. I know precisely what is in the kit I designed and why each choice was made (and yes there were cheaper alternatives). I haven't done the in-depth research into each and every "new" option that has come onto the market since - no longer in the trade so to speak. That said when I was doing the design work there was more than one option, the system I designed was the best balance of quality, reliability and value I could put together, with safety being a major concern.
If you haven't or aren't willing to take the time to make a similar effort, my point is that up front price alone is a very poor criteria on which to base a decision, to have the work done for you is I believe of value. If you don't agree you will make your choices accordingly and take responsibility for the outcomes.
Note that the supplier of the O2 bottle and regulator, in the kit I designed sell a large range of other gasses in disposable bottles, all the rest of the range have a different thread/regulator to prevent dumb mistakes (***** proofing?)
The Bossgas regulator (assurances by the retailer aside) is listed by the manufacturer (RocFly Shanghai) as a Argon/CO2 regulator with no mention of O2 compatibility.
The other point is that the everything else being equal the diameter of the diaphragm in a regulator is really one of the critical determiners of the regulators accuracy and life expectancy. When the diaphragm goes not only will it (or the whole regulator) need replacing, you will almost certainly loose the contents of the bottle.
Sometimes size matters and one is nearly twice the size of the other - you guess which is which.
I wish you luck with your purchase, but there are real differenced between the various offerings and very good reasons why the prices are different.
And don't some of you guys amp up when anyone suggests that being a tight arse isn't of necessity an unqualified virtue.
Make your own decisions but make sure they are informed decisions that take all the factors into account, not just price - which is what I said in the first place...
Mark