These ones are straight from a White Labs’ WLP007 pack. ‘Outsourcing’ the lab work, making it incredibly simple. They know what they’re doing. Or make a nice clean starter with your strain(s) of choice and store the same way. The cryovial caps are screwed on tight. They can handle a little pressure, but I haven’t noticed any building up. I recommend just pitching one vial in a 50-100ml first step starter, for simplicity, but I actually just use a loop’s worth to inoculate 10ml sterile wort then step up to 100ml, 500ml, for a half batch, or step up again to 2.5L for a whole (5G) batch. Half batch then repitch is best, if you have time to brew another batch soon enough.