This comes up all the time: standard ordinary laser toner is magnetic and will be read by the banks. The gotcha is that standard laser toner rubs off in the *very* high-speed sorting equipment that are used, and this makes read rates drop low and the banks will hate you.
I researched check printers for a customer, and was surprised to find this. The Troy(tm) printers he bought are basically stock Ricoh engines that have slightly tighter paper handling (for registration), plus they add a proprietary Teflon-type powder coating on the output path to coat the checks.
I saw some examples of checks printed with and without this special coating after running through something like 40 passes through check processing equipment, and the one without the coating was a mess. These require special handling that the banks do *not* like. Apparently, they go after companies that issue these kinds of checks with special processing fees.