It's cheaper, adjustable, has better quality kydex and leather, no cross on the clips and replaceable shells over the CBST. I'm not sure why anyone would buy the flimsy CBST over the OF holsters since they also have a 50 year warranty and if you don't like it in the first 30 days, they'll refund your money and you keep it free of charge.
I originally bought one for my Shield, bought an XDS to try out and liked it better so I bought an XDS shell. The XDS got recalled which isn't sounding too good from those that got them returned so I ordered a G26 shell for my current carry gun. If it was a CBST, I would of had to buy 3 holsters at higher prices and long wait times in between each one.
I can't recommend them enough.
ETA: I agree to go the DIY kit since it's much cheaper, easy to assemble and easy to customize.
Here's my OF holster with the newest G26 shell I had to trim up. I noticed they changed the outer texture of the kydex now to smooth, but it's still just as sturdy.