i currently have the nembo daytona. it falls short in many areas, imho. while around 320USD with shipping included for this JF model, i think its quite worth it to get this&i am fully intending to do so once the christmas/new year shipping craze has died down. here's why:-
base nembo daytona - around 100USD-130USD (depending on whether you get it from m2m or from the man himself.)
sapphire crystal + gasket - around 60USD to 100USD (depending on where you get it from. clarks, a old SD, a crystal maker, etc.)
relume - around 100USD-150USD (depending on who, what type of lume)
total for the above, even at the lower end, is about 250USD excluding any additional labour & shipping cost which may be incurred. but even with the above mentioned mods, it still leaves you with a wonky bracelet, weird dial, fat chrono pusher guards, etc.
IF, which is quite a big IF, JF has finished these 21J/23J daytonas the same way they did with the 7750s. i feel its worth the additional 200USD, compared to the nembo.
just my 2cents.