This isn't really true, no offense. A lot of the clones can be upgraded, they just advertise them that they can't as these Chinese companies don't offer tech support. Myself I wouldn't risk it, but there are reports online of people upgrading them. Ignoring that though what exactly would you need upgraded firmware for? Most of these flash carts run 100% of the games within the first revision or two so imho, so while the option to upgrade firmware would be nice, it isn't even close to being an essential feature. So yeah, they are just as good.
I mean the tg16 card I just bought was only 30 bucks. I saved SEVENTY DOLLARS buying a clone. It's based on an older revision of the board but still runs 100% of the games so while firmware upgrades would be nice can you, with a straight face, say they are worth $70? Now if the cards were priced reasonably, at like 45-50 I probably would buy the original, but the creator is greedy, so he doesn't get my money.