I just weighed my new front diff with OFNA 120,000 wt oil. Complete with outdrives but without the pulley. 35 grams.
The spool, also with outdrives but without the pulley, weighed 20 grams.
I hope it's not too much of a weight penalty. I've always felt that a diff suited my driving style better than a spool. But I suppose the new tiny TM diff is as good as it gets