In my experience, Chris and Ron make some dang good parts. Yes, they are
pricey; yes, there is usually a waiting list, but you get what you pay
for!!!  I have never had issue with any of their units I have come across.

My opinion, anytime you change gearing for a specific application, you need
to take into consideration several things: weight of your vehicle, driving
style, horsepower and torque curves (RPMs) and tire size.  Adding an
overdrive gear can be beneficial if you wish for better cruising rpms.
True, as posted previously, you do not want to get into a situation where
you are lugging your engine, but if you have made power mods to your engine,
changed tire/wheel size, or find you do more highway driving than a 4 speed
is comfy with, a swap may be a good idea.  I have installed gear splitters
in 4x4's several times over the years, sometimes with an over drive, usually
with an underdrive for towing.  I am swapping a close ratio 5speed into my
Cabriolet this winter because I want a better ratios to use the added power
of an engine upgrade...as well as a swap of a higher 5th gear because I do
plan roadtrips with the car...thus I want a 5th gear putting my engine into
the wide torque band at 1800 to 2000 rpms rather than at 3000rpms.

My only gripe is I have not been able to convince my own brother-in-law
(Ron) to make a gearbox for my watercooled VW!