Yes, mortgage advisors used to be people to approach very cautiously but recent legislation has weeded out most of the rogues and they tend to be reasonable people to deal with. There is no fee for you but the broker gets a commission (£200 or so - it will be declared on one of the forms you sign if you take out the mortgage) paid by the lender.
You do need to be wary of deals offering "no arrangement fee" as they could well charge lots for the valuation or for something else. The important figures are the total of all the lender's charges and the monthly payment.