Do it yourself mate. Really easy. Unbolt your chair, bolt the swivel plate to the seat base and then bolt the chair to the swivel. Drivers is a little more involved. Depending on which swivel you use you might need to lower the hand brake.
Hi got factory fitted second battery and intended to fit after market swivels.
Main reason for this was due to factory swivelling seat do not have height adjustment.
So found that the base of the swivel will touch the rubber cover of the battery . The swivel could be spaced up by about 15mm and should then clear the battery and swivel fine.
I decided not to do this due to the missis only got little legs.
Put it back together and waiting for a manufacturer to solve the problem for me ,fingers crossed.