5 Speed onto cassette hub 120mm OLN

[Fastpedeller]

I've seen a couple of products which may be useful to those of use who have older frames, want to convert a fixed bike to gears, or prefer not to have too many 'extra' gears. Basically a hub with cassette facility with OLN dimension of 120mm.
The following links describe

http://www.bikerumor.com/2013/09/19/ib13-fyxation-...

http://sunxcd.net/hubs/

http://janheine.wordpress.com/2013/09/21/grand-boi...

The only issue I can see is that they seem to have an alloy cassette body, where steel would be a lot more durable for very little weight penalty.
Could be the answer to getting many an old frame back on the road, or getting a very strong wheel without the dubious extra cogs and high cost chains that go with them?
What do other think?