I never really quite liked Unisoy from the first time I tried it. It didn't really have the full "milky" flavour of real soya milk and my milk was a little lumpy because the powder didn't dissolve properly.
Also, I think Unisoy processes their powdered soymilk too much in an attempt to make it healthier, ruining the taste of the soymilk. I also didn't quite like the idea that soymilk could be made in the powdered form as real soymilk is much harder to get (in other words, much harder than pouring hot water onto powder from a sachet.)
I wouldn't recommend Unisoy, but I suppose I'd drink it if I had a sudden, urgent craving for soymilk. Besides that, nah.