there are advantages as well as disadvantages in doing vipassana in jhana
advantages: the mind is more maleable in deep samadhi so any insight gained will strike deeper and last longer
the samadhi component is already well developed so there is no struggle to build that up like in dry vipassana
disadvantages: you may not see impermanence of the world you normally inhabit ie the kama loka, but only see impermanence in the rupa world/jhanas. Hence not letting go completely, hence getting stuck at certain levels of progression. If a person's wisdom is penetrating enough to see the symbolic nature of seeing impermanence in one thing being (mind door) applied to everything (6 sense doors) then it would be less of a problem.
Because of the deep samadhi it maybe difficult to see impermanence and as there is little that one may observe as the self- difficulty in understanding non-self.
I would leave this to the experts who have already attained stream entry and understand the impermanence of all phenomena already. Their minds will be more amenable to limitations that this method poses but are well placed to make use of the advantages it offers.