RO units, in my opinion, are a must. Most local fish shops (LFS) have RO water for sale, but the expense of regular purchases will eventually exceed the expense of a one-off purchase which you will always have immediate access to.
Additionally, you may be lucky enough to have a LFS that constantly monitors their RO/DI water TDS, but more than likely it is in high demand and is very easy for their levels to exceed what you would like to put into your tank.
You will need to monitor your water produced regularly, and you will need to change your filters as and when required. But this is a simple process and potentially only needs doing twice a year, again depending on your tap water TDS.
The perceived technicality of the RO unit can be slightly intimidating if you are looking at pictures of them, but have never used one. I felt the same too, until I purchased my first unit and realised how very easy it was to connect up and use.
Hopefully this has explained a bit about RO Water for aquariums and how they may benefit you.