The more expensive bike has MicroSHIFT Advent gearing which I gave never heard of. The older cheaper uses a Deore rear mech which are time proven. So technically I would save the Ł100 and invest in good cycling shorts and naybe a pair of cycling shoes.
Key thing when buying a cycle is SIZE, go on the Cannondale sizing chart, determine the correct size for you, then buy that one. Don't compromise and buy “ what they have on offer”
http://yarta.innovations2019.org/can...ke-size-chart/
Steve