They look similar in the 2 C battery versions except that the ML50T has a side switch and 3 modes versus the 25LT twist switch and only 2 output levels. Due to the side switch I note that the 50T is a bit longer per the Maglite web site. Also in high mode it is listed as considerably brighter. Are the heads and light cones similar?
I now have both. Due to the side switch the ML50L 2C is about 1.5" longer than the ML25LT. Tail caps are interchangeable but the tail springs are slightly different. The 25L has a head diameter of 43.2mm and the 50L is larger at 50.1mm. The current 25L has 2 levels of output and the 50L has 3 levels. The ML25L lists max output of 192 Lumens and a beam throw of 337 meters. The ML50L is brighter at 466 Lumens max but has more of a flood beam at it’s tightest so lists beam throw of 291 meters. I personally prefer the ML50L beam as it does not develop the large doughnut hole in the center that the ML25LT does at wider beam adjustment settings. It’s lowest setting is also lower than the 25L’s and claims a maximum run time of 109 hours versus 72 hours for low output on the 25T.
The 25L appears to use a much less efficient LED as run time at 192 Lumens is listed at 7 hours while the 50L claims 8 hours and 15 minutes on high beam. Not run long enough yet to see if the 50L longer run time is due to output reduction due to heat buildup, definitely a possibility.
Overall I prefer the 50T unless compactness is a primary concern in which case take a look at the current 2 AA Mini Maglite Pro which is brighter than the 25L at 332 Lumens max and has a better beam pattern in my opinion, more of a flood beam available when wanted. The Mini Pro and 25LT are close in overall length. If familiar with older Mini Maglite’s the Mini Pro has a redesigned head with a much deeper reflector design and offers two output levels. It also has a lanyard attachment point, something missing on all the larger Maglite lights.
I would add that all these Maglite models do not have mode memory and come on in high mode while I personally would prefer that they come on initially in lowest mode as a help in preserving night vision. Also advantageous for use in the house at night to reduce bothering others.