No negatives that I've found...
Here are my own experiences of a SAIC TF135 that I bought in Sept 2018 with (it turned out) 'checksum ecu error', over sensitive noisy engine fan running continually and a high 950+ tickover. A couple of professional ecu specialists thought the Continental ecu was 'broken' - this alongside seized brakes, plug gaps 'everywhere' and a blocked air filter meant that I had a lot to do to get the car up to standard.
I chose a standalone 'sporty' remap to replace the ecu and received a used NNN100743 Motorola MGR, intent on avoiding the costly new ecu and expensive remap service at that time.
Earlier this year I bought into PScan and used it to synch a standard (brand new) SAIC Continental ecu (NNN000830) to return my car to to 'stock SAIC' - with no checksum, frantic fan + idle etc - keeping my sporty remap as a known good spare.
A pal on the forum 'went the other way' and SAWS remapped a used NNN100743 since his own SAIC ecu exhibited these same faults (as do others, it seems.)
At this time, as well as my stock Continental SAIC, I bought a used NNN100743 MGR Motorola, stock TF 135 mapped, and ran it absolutely normally in my own SAIC TF without checksum error/frantic fan + tickover using PScan to synch it successfully.
So, MGR Motorola substitution seems to be a cost effective way of removing the SAIC 'weakness' or, indeed, one can invest further in the SAWS upgrade via PScan. As PScan says the software can be easily modified to support the 'cooking' hardware, in my case NNN100743, but not 75/Freelander applications.
We've found that SAIC ecus cannot be remapped via OBD (perhaps this interference causes checksum error?) and fix or remap might only be by chip replacement - except the abundance of the 'more solid' Motorola renders this a better/sorted v-f-m route, imo
I hope this enthuses similarly afflicted SAIC/Continental owners and standalone-remap-requiring Rover/TF owners...