Go to Bristol Flying Centre. They have two CRE's there teaching and examining on the 525 and have dispensation to reduce the amount of training to an appropriate amount if you have adequate experience which saves a lot of money and time.
The 525 is split into 3 groups with regard to difference training -
1 the straight CJ or CitationJet,
2 CJ1 and CJ2,
3 CJ1+, CJ2+, CJ3
You require difference training to transition between these three groups and the normal path at Bristol would be to train on the CJ because it is the cheapest and do a short difference course to fly the CJ1.
Bristol Flying Centre
Hope that makes sense
Tom