Has anyone ever hiked to the Mantova or Gnifetti Huts without using the ski lifts?
I heard that you can hike from Gresonney and that it takes about 6 hours, but can't find much information about how technical it is, actual hiking time (for medium fitness), scenery en-route, etc.
Any advice or info much appreciated.

Personally - I haven't.... I did the hike to Signalkuppe using the cable car on the Italian side... but the folks who were with me did mention that it was common to do the whole climb starting at Alagna and reaching the so-called Passo dei Salati on day 1, before the cable car system was established. It is a long hike, and some folks still do it that way.