Career development loans are run in conjunction with two banks. They are commercial loans. As such, if you are taking out other loans, it is quite likely to have an impact on your overall credit score.
The advantage of CDL's are that the interest is paid for the duration of the course. However they do have an upper limit of £10,000 which for flight training is a fairly limiting sum. The interest rates are around 10% which can make them more expensive than the better commercial products, if they are maintained after the interest paid period.
It is often suggested that a CDL should be repaid within one month of the course (qualifying period) ending, and substituted with a loan with a better interest rate. A good idea, but often not as easy as it first appears, since the consolidation of existing loans often attracts less favourable rates of interest on an unsecured basis.
There is a Q&A factsheet
here which is worth a read through.