While there are a lot of wide clincher rims available today, these stand out together with current Pacenti Brevit rims as having a shiny finish and shape profile that mimics traditional tubular rims. The Mod4 rim's 25mm external width was among the widest touring rims, perhaps wider than any other brand's double-walled touring rims (before Sun Rhynolite rims were later released).

The Mod4 rims are crazy strong, but with their staggered spoke eyelets they do not get as much in the way of spoke bracing support, compared to rims having their spoke holes all in a straight line.
One result of this is that there may be brake pad rub, which is made worse by the rim's extreme rigidity (which mirrors any lateral displacements about the loaded contact patch 180-degrees up to the brake pads).
I replaced similarly-wide aluminum single-walled rims with these Mod4 rims, and was quite surprised by the above tendencies.
A solution for the above lies in the use of wider axle widths and flange spacing, and the use of narrower freewheels to limit wheel dish. So on wide-spaced tandem rear hubs (having a "traditional" numbers of cogs concurrent with these rim's 1970's introduction), the mirrored flex up to the brake pads would not be noticeable.

The Mod4 shape profile was also used in a 26" (M261) rim variant that was seemingly the preferred choice for the nacent sport of downhill MTB racing.

Mavic over some short period of years went on to produce even wider versions as well, the M5, M6, and M7 Rondo rims were based on the same profile shape but their external widths ran from 27mm to 32mm. Some of these may have been only available in 26" however.
I believe these were by far the widest double-walled rims made as of around the late 1980's or so, presenting a stunning appearance.

Mod4 rims can be 36, 40 or 48-hole, and were replaced by the taller-profiled A719 rims which had similar inside width but a slightly narrower machined outside width. The A719 kept the spoke holes in a straight line for better spoke bracing on modern, more heavily-dished wheel builds having wider stacks of cogs.

Prior to wide rims having been considered desirable for road bikes, I would inquire with all of the rim vendors at Interbike year after year, and the vendor's response to my inquiry about wider "road" rims was often met with a look of "are you crazy" (wider rims being seen as heavier and less-aero, and of little benefit to a 23mm tire).
I recall REAL as one maker who around 2003 touted their newly-widened rims (of at most 15mm internal width) and who seemed to take me seriously (I have their shiny rims on my Litespeed Siena).
I kept an eye out for many years looking for more Mod4 rims to build with, my current inventory including four built sets, one set being 27" and two being 700c on cassette hubsets. A final set is built onto a flashy pair of solid-hi-flange Specialized tandem freewheel-style hubs to which I retrofitted hollow axles, 126mm in the rear (lives on my Trek 720 limo).