For those who use IB: How long have you been using them? Do you use their client or their API? Is it alright to use both, in parallel? People complain about

For those who use IB: How long have you been using them? Do you use their client or their API? Is it alright to use both, in parallel? People complain about their customer service; have you had any problems? Is it easy to transfer money to/from your IB account?