In my experience, they have only two advantages - enable you to use low range as a creeper gear on hard surfaces without windup, and allow you to put off replacing a dodgy front prop shaft by only spinning it at low speeds.
I have them fitted to the 2a, and last year I did the trip to Sydney one way with them engaged, the other with them disengaged - the difference was not perceptible in either handling, noise, or fuel consumption. They stay engaged about 90% of the time.
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
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