I read somewhere that there are 2 types of ECU, an HW and a SW or something like that......
I believe it is quite important not to use file one on the other type, I'm sure someone will clarify....
2003 2.2hdi estate - mine 1998 Volvo 940 auto estate - also mine 2019 Citroen C3 something - the wife's PP2000 user, can help with faults / diagnostics in the Bournemouth area.
In answer to the checksum question, when you READ an ecu file, or OPEN a file prior to DOWNLOADING it, the lower left window, "Programming Data File", will show the Checksum on the 3rd line down. To ensure you have a good copy of your original, READ it twice, ideally saving it on separate media and make sure the Checksums are the same.
With 2.2 HDi's, there only seem to be 2 ecu variants, (semi-mux and full-mux), that you can't swap ecu files between. With 110's, perhaps because they were produced over a longer period, there are definitely more incompatible versions. The more similar the age of the two cars, the better the chance of a match. If the hardware and software codes, (lines 2 & 3 in the "ECU Data"window), are same it should be OK.
2002 HDi 2.2 Exec Estate, (2008-12) (wonderful)
2003 HDi 2.2 6-speed Exec Estate (2012-19) (also a gem)
2009 Citroen C5 2.0 HDi VTR+ Estate (godawful heap)
2008 BMW E91 330i touring (great fun - murdered by a reversing SUV)
2007 BMW E91 325i touring (slower smoother quieter)