Dick/25 Jul 12 - 03:19 PM
" This technique is also used by classical pianists.."

There are always people who use this or that with more or less reason.
"Strengthening" exercises has been a matter of fashion with pianoplaying on and off. What I said above is basically the same for concertina playing and piano playing. For the average and healthy individual there is not much reason trying to improve "strength" by any extra "work-out". For extreme/competitive performance having some extra finger power and endurance of course may be beneficial but always keep in mind that for all performance with musical instruments problems from over-use and strain are a lot more important and frequent than any "strength" issue.
Some specific exceptions do exist. For the left hand guitar ( or similar) work which may be *static* to a major degree strength 1) may be of importance and grip training may thus be motivated.