Bug fixes. All 2.x before 2.3 has hardware issue that can prevent it from working on some PCE and TG-16 that has accessory added to ext port. 2.3 were issued directly to people who bought 2.x and had problem, 2.4 is released in stores. If your 2.x is working fine with PCE and you have no plan to add CD-ROM system or any accessory, you're OK. Duo are also fine. If you have TG-16, you should contact Krikzz for exchange just to be on the safe side.