The unit you have in the pic looks good:
2. has tds meter. I can't tell if it's a single or dual tds meter. If it's single, you might want to see how much extra for a dual. On a single, depending on where the probe is positioned, it'll help determine when RO membrane OR DI chamber needs to be changed, but not both. A dual meter will allow you to position a probe between the RO to DI stage, and the 2nd probe after the DI stage. IMO, probably worth it if it's not too much to upgrade.