Is the Manley Steelhead still relevant?

Yes, yes it is.  

Absolutely. It gives you quite a lot for the money. If you get one and put super low noise tubes from RAM Audio Labs in it you can not do much better without spending frightful money. 

Look at TW Acustic RPS100 much better sound and build quality.

ebm, it better be as it is way more expensive. I do like that it has a balanced input. I do not like that is has 2 12AX7s in it. All the phono amps that I have listened to that have 12 AX7s have been colored. I know the Steelhead is not. I have not heard the TW.