"Most lobsters available are opportunistic omnivores. This means they will occasionally eat anything that presents itself a target. The second big issue it most of these lobsters do get large and live for quite a while. Thirdly, they are nocturnal and fairly cryptic.
I would personally lean...
RO + DI.
RO alone - TDS reading 004
RO + DI - TDS reading 000, which is better
(It also all depends from where you like and from how good of a water your city has)
Getting a complete unit w/ DI isn't much more expensive than an RO alone. I would invest the money if I were you.
As a matter...