If it's not costing you anything (fee / worse rate) always go with a mortgage adviser. They usually deal with a different department in the banks which has more senior staff and quicker approval times...
The wife works for a large UK bank and has knowledge of these things - they definitely do have different departments dealing with MAs over people doing it themselves...
Your MA should diarise himself to call you in five years time to discuss the next deal. This could be complex, your situation could be totally different. If you like the MA, use them again, let them get their commission. Don't do yourself what someone else gets paid for at no cost to you.
If it's not costing you anything (fee / worse rate) always go with a mortgage adviser. They usually deal with a different department in the banks which has more senior staff and quicker approval times...