I have both and the caddy works fine if you add a pad to the top of the bucket, the rolling seat is much more comfy and the height is good for me. I use the rolling seat more often than the caddy for detailing, but use it for washing all the time.
After reading some of the responses I am going to see how I can use the seat for sitting & MF storage and attach the caddy somehow for the product as I agree they tip over on the bottom shelf.
Can't go wrong with either, but my experience the seat is the ticket, at $69 great deal.