I just wet tested both of these tubs on Saturday. Prior to the test I would've picked the Chelsee. After the wet test the J-365 was the clear winner and is getting delivered on Aug 29th . I didn't experience the floating out of the tub as you did, but I did find the jets didn't produce the deep massage feeling I was looking for. I agree with John, go with the one you enjoyed more on the wet test.
FYI.... I think there is one less diverter valve on the Chelsee which may have made a difference in power to some of the seats.
vg13