Synology - But look at ReadyNAS Seriers
I must precede my recommends by stating that my experiences are from home use, not from small business or school IT perspective. However, if you want to spend less time setting up the NAS & maintaining it, then read on.
I recommend Synology for it's web based GUI which is, to me, outstanding. Period. Easy to use. Well written and informative Users Guide, too. Time Machine is a piece of cake to setup - here the steps from the Users manual:
"Synology DiskStation provides compatibility for backup with Apple Time Machine. Mac users can back up their data to Synology DiskStation's shared folder without problem.
To set Synology DiskStation as Time Machine's backup destination:
1 Go to File Sharing > Win/Mac OS and tick Enable Mac file service.
2 Choose a shared folder from the Time Machine drop-down menu. The chosen shared folder will become Time
Machine's backup destination."
I have a D-Link 323 which has to be hacked with the "funplug" s/w to get afp and Time Machine capability. I can't recommend for your situation.
I almost bought the Netgear ReadNAS Duo because of it's Mac Time Machine compatibility. But, it's expensive w/o a robust user interface.
The tie breaker for me (Synoglogy vs ReadyNAS) was the information on the company's web site and the Users Guide. (I downloaded both to compare.)
Finally, think about several NAS units as part of your risk management. For your 50-60 users, if one machine or the disks goes Tango Uniform, less users are effected. BTW, although I haven't tried it, Synology has backup procedures for their NAS, too, described in the Users Manual.
OK. My 2 cents. Measure twice, cut once.