It's not exactly a con as such, more a meaningless marketing gimmick. A manufacturer wanted something to differentiate their product from the almost identical products from other manufacturers and there's not much you can add to a toothbrush. Lather on the advertising flimflam and you can suck some customers away from your competitors who don't yet have the SuperNewThing on their products.
There is a point to brushing your tongue, but the bristles that you use for brushing your teeth do a better job of cleaning your tongue than a few little flaps of rubber stuck on the back of the toothbrush.
£3 electric toothbrush from Wilko's for me. Does the job well and it's cheaper than the lower end electric toothbrushes with replaceable heads (due to the cost of the heads and the lower reliability of the more complex toothbrushes).
I tend to sterilise my toothbrush by pouring boiling water over the head sometimes, when I've made a mug of tea and there's some boiling water left over. Anyone else do that?