The MTSs was designed to hold temps steady for single step infusion mashes, but it was not designed to ramp temperatures in a multi-step mash regimen. Furthermore, the MTSs does not require circulation, in fact that would result in additional heat loss.
The best way to envision using the MTSs is essentially matching your strike water and grain temps up for a single step infusion mash, then adjust the set-temp on the MTSs to hold your desired mash temperature until you are ready to lauter and sparge.
Conversely, In a typical RIMS tube setup; a high wattage heating element (2500-5500 Watts) is placed within an ancillary loop and wort circulates through to maintain temperatures (single step mash) or ramp temperatures (multi step mash), typically in a non-insulated mash tun.
In comparison, a HERMS setup recirculates wort through a stainless steel coil mounted in the Hot Liquor Tank (HLT); which in turn has the ability to be heated to a temp differential that will raise the temp of the recirculating wort.
The beauty of adding a RIMS/HERMS setup to our infusion line of mash tuns is that ramp speeds will be extremely quick as a result of minimal vessel heat-loss. As a result, if you decide to go with a RIMS/HERMS setup, the MTSs will not be required since the higher wattage of the RIMS element, or the temp differential of the HLT is plenty to overcome any heat loss from the vessel or recirculation loop.
Depending on the typical style of brewing that you gravitate towards, a single step infusion mash may be all you will ever need. In that case, invest in the MTSs and it cost effectively automates your mash process. Yet if you desire the additional complexity of a RIMS/HERMS system and multi-step mashes, then by all means shoot for that setup since they are mutually exclusive systems. Just remember that a RIMS tube or HERMS system will require ancillary brewing equipment such as a pump, coil, 115/220v electrical temperature controller, RIMS tube, element, and hardware to name a few.