Interesting that most here are recommending the M520 when on most other forums the consensus is the M540 is well worth the little increase in cost. Maybe tourist don't stress the gear as much or are just too cheap .
The M540 upgrades to better bearings , better seals for the bearings and the spindle is chromoly instead of plain steel so they last much longer than the M520s.
You can find the M540 on sale for less than $50. They are $41.99 at Nashbar right now.