I have several 5 speed freewheels in excellent to new condition on various wheelsets. The IRD is the cream of the crop. When I put a 13-28 5 speed on my 1973 Competition it completely transformed the bike. It has Shimano-style shifting ramps that really make friction shifting not only faster, but also reduces the "over-shifting"* you sometimes have to do shifting to a larger rear cog.

I bought my IRD at Harris Cyclery and they recommended a narrower 8 speed chain to better take advantage of the shifting ramps on the 5 speed freewheel. Works great and it's all silvery nice too!

One more nice thing about the IRD is that it is removed using a standard Shimano cassette removal tool and this design allows you to get down to a 13T cog whereas before I think I was pretty much cut off at 14T, though I now notice that it looks like the vaunted Suntour offerings also have 13T. Anyway, I really like having the slightly taller 52x13T for downhill fun over the 52x14T I used for the first 35 years on this bike;-)

*over-shifting = where you have to pull back a friction shifter a little too much to make the shift and then trim it forward to better align the rear derailleur under the newly selected cog.