You won't get a conclusive answer to your question because so much depends on your circumstances and objectives. Any Financial Adviser will need to ask you a lot of questions before giving an opinion, but that's all in your own best interests.
This is not a cheap way of doing it....
although the APR may be low, the period is usually a long time and so the amount you are actually repaying is more...
eg A loan of �10,000 taken over years at 9.9% APR total repayable �11,520.68
The same loan taken over 10 years at 4.9% APR Total repayable �12,593.60.
Also bear in mind that the 3 year loan would be at a fixed rate whilst the 10 year loan would usually be variable.
Of course it's a cheap way of doing it at a rate of say 5%, and you can pay it back any time you like at any amount you like, assuming you have a "decent" mortgage.
Fair point Oneeyedvic, but in this instance, I refer to one which allows you to pay back at least some of the capital without penalty. Which is most of them these days.