IST is a cheap brand. Things are good enough. Nothing brillant.
I've also used an IST Sidemount similar to the one described by @Michael Shamrock and I've found that it's hard to release air from the bladder and from the bladder bag. I had to use it with the zipper partially open to avoid the bladder bag to keep air inside.
Some time ago I bought an IST swimmer mask, and had to change for a Technisub AquaSphere as it was flooding constantly.
I've also used an IST Sidemount similar to the one described by @Michael Shamrock and I've found that it's hard to release air from the bladder and from the bladder bag. I had to use it with the zipper partially open to avoid the bladder bag to keep air inside.
Some time ago I bought an IST swimmer mask, and had to change for a Technisub AquaSphere as it was flooding constantly.