I was a lawyer advising startups. The biggest issue with platforms that try to connect the two groups is that it becomes a race to the bottom. Startups using services like the one you are proposing typically base their decision on who to use almost entirely on price. This is never good for the lawyer who (speaking for myself only) wants to provide a good service, build a relationship and get to know the person and their motivations in order to properly understand their problems and advise them.
This is a very real concern. When a client can compare the pricing it does become like that. However, do you think client acquisition is a problem for practices like yours? Is it actually hard to do?
