The optical specs for the 24x WF and MC are the same. Those eyepieces have the same optical formula, the main physical differences being in the housing to hold the twist-up eyecup of the MC.
The MC eyepieces are supposed to all be fully multicoated. The WF eye pieces, when very old, may be single coated but I think mine and others I've seen have been a mix of single and multicoated elements. Nikon updated the coatings of Fieldscope eyepieces in the course of production without announcing the changes. That said, I've not been able to discern a practical difference between any of the fully multicoated MC eyepieces and their older WF counterparts. For example, I happily interchange an old 27/40/50x WF and a much newer 27/40/50x DS without seeing any difference in optical performance (and in fact, I prefer the WF because it is much smaller, making it a particularly nice match to the Fieldscope 50ED).
Transmission through any 24/30x WF or 24/30x MC eyepiece, as well as through the non-wide 20/25x (of which later production, I think, was fully multicoated) will be excellent because these designs have relatively few optical elements compared to any of the other Nikon WF, MC, DS, or zoom eyepieces (all of which have a built-in barlow). Compared to the 16/24/30x DS, which is a unique new design, the 24/30x WF is physically _much_ smaller and lighter, has slightly less eye-relief, has the same FOV, and has a very slightly curved field. I find that the 24x WF and MC design retains its optical performance better than the DS when the eye is not perfectly aligned with the center axis (in other words, the WF/MC design is more forgiving of eye placement), so I prefer the WF for rough and tumble birding.
