73 is just an airplane, but the cockpit is very busy and "switch intensive"... in order to retain the original type Boeing has kept the 73 firmly rooted in 1965. If the ERJ is anything like a brasilia you'll feel right at home.
Bus is a whole new philosophy. You either need to be very smart or have a good training dept that knows how to teach bus to normal pilots. Otherwise it will suck to learn. But once you learn it, it's very easy to fly, there's a reason it's senior to the 73 at most dual-fleet operators.