I am actually going through this process at the moment. In theory it is either or!! I wanted to do my visa on income alone which is perfectly acceptable. The catch 22 for me is that for proof of income it requires a certificate from your embassy, I am British but the British embassy no longer issues these certificates. I have spent the last 15 years in France declaring income for tax purposes there so I asked if they could issue me with a certificate - no reply!!! I am going to the bank this week to see what the manager proposes but I guess it will be go down the
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0 route with the agency providing the money (for a fee!!) and buying the bank insurance (although she couldn't tell me what it insured!!).