Pro's.......safer, quicker (make more money in less time)....
Con's.....requires a certain amount of on going maintenance......somewhere to store tank and RO...(a DI on it's own is a bit pricey to run all the time)
Conclusion....no contest really......why not use a bit of both ?...though I think you'll find that you use the pole increasingly more often.....the higher purchase and running costs are more than paid for with the increased volume/earnings.