I just got a new bike for my son (he's going to secondary school and needs a better bike), and was surprised to see how many kids' bikes came without fenders. What's up with that? Who wants a serious bike without fenders?

Of course most bikes still come with fenders, but that's also a major limitation for this device: you've got to remove your rear fender. Maybe this device acts somewhat as a fender, but the site says you can't use it in heavy rain, exactly when you need that fender the most.

Being cynical I would say it is yet another way to upsell.

Here in Germany if you want to get a cheaper bicycle, other than flea markets, usually they make you mount the pedals yourself, doesn't have fenders, lights might also be missing, depending on the offer.