I agree with touring first. I would tour to see which area works for me and where I would feel comfortable, that is what I did and it took me about 6 months. When I toured I stayed in short let accommodations all over London. I'm still in a short let apartment now.
I think perhaps there maybe is a higher number of clients compared to other regions but London has a large population plus Living costs, travel and rents are high. I would say London has been OK for me, not great but OK but as I have never lived anywhere else I cant really compare the difference. But I know that If I wanted to move to London from another City or Country I would take a chance and go for it.
The bonus with short lets is that you can always cut your losses and move on if it doesn't go as well as planned and they don't require as much documentation ie bank statements, employment references as a a long term rental property does. The required deposit and months rent in advance plus your ID (Valid Passport) is usually enough.
Downside is that they are more expensive to rent but the longer you stay the cheaper they usually are.