I have the Izula, F1, S1 and WM1
Also Zytel. Falkniven leather and aftermarket sheaths for the F1 and S1, and Kydex for the F1
I was initially against the Zytel sheaths but they have grown on me. They are the lightest possible, lowest profile and no maintenance. if they get wet - the water just pours out. They are wll enough aired that the knives will not coorode because they are in the sheath. Also when on the belt they keep the knife accessible without dangling down or getting in the way. there is also pretty good retention with just the clip in the sheath even without suign the strap. This means the knife can comfortably be pulled in and out of the sheath for multiple small jobs one handed easily , and the strap put on when travelling or other and what it doubly secured
I'd consider the Izula to be more of a match to the WM1 than the F1
Overall the F1 is the knife I would like most to have to wear and use all day every day, for overall useability it is hard to go past the F1. The F1 in Zytel would sit on the belt or in a cargo pocket and almost be unnoticeable but at hand when needed. That said the Izula and S1 would be a good combination - the S1 is still only as long as a steak knife but has just enough weight to start thinking about swinging it rather than just slicing.
Hmm I may think of putting a slice of Neuroprene in the bottom of the zytel sheath