What HP says about these units:  

The high speed, energy efficient M501n helps save money and time. Its combination of fast print speeds, compact size, high quality and fast print speeds mean that, not only will the M501n fit seamlessly in to your existing set up, it will increase your offices productivity and save money when it comes to associated printing costs.

Save money, up productivity
The large 1200-page capacity allows work to flow uninterrupted by the need to change paper. The large capacity also allows you to print unattended, knowing the paper wont run out. Likewise, the high yield cartridges last for up to 18,000 pages. HP's anti-fraud cartridge authentication technology protects you from substandard cartridges, ensuring you get the HP quality you pay for.

Safe, secure printing
Protect against data leaks with the M501n's security features. PIN printing through an optional USB drive helps to ensure that documents will only end up in the hands of whoever printed it.

With the rise of mobile and cloud computing, security has become more complex and challenging. While you may benefit from a multi feature printer, the increased usability can make your printer more vulnerable to security threats. The M501n is compatible with HP JetAdvantage Security Manager, allowing you full control of security for your HP fleet. Managers and security officers can easily protect against sensitive data leaks by employing a single security policy across the entire fleet