I must reiterate what Mike said, many people over tighten the collets, if you have difficulty loosening the collet with two spanners, then you have over tightened. There isn't any point in asking which system is better, it's up to the individual to try both methods, at least with the spindle lock there is less chance of over tightening and causing damage to the collet. It would surprise many members as to how little force is required to perfectly lock the collet onto the cutter. Whilst I don't recommend anyone attempting the following, I recently tried it to prove or disprove what I had been taught, that in the table, if the cutter come loose it will just sit there safely.
I switched off the power to the shed, fitted a damaged cutter into the Triton router in the table, finger "tightened" it, switched on the router, stood outside the shed and put my arm through the doorway and switched the power on. The router started as normal and after about 15 seconds during which no unusual noises were heard, I switched the power off and examined the router, the cutter was still in place, so you must arrive at your own conclusions.