My understanding is the beam forming still functions on a limited 450m you just do not get multiple beams? Has anyone compared performance of PMP450m Limited and PMP450i Sector in a noisy 5GHZ or 3GHZ environment?
You are correct. The only thing that is limited is the "Multi-User" portion of the radio feature set. Otherwise, it functions the same as the Full 450m cnMedusa AP.
You still gain all the benefits of the antenna array, including improved sensitivity on BOTH the downlink and uplink (from beamforming), simply to a single subscriber per time slot.
In fact, you can see what Massive Multi-User MIMO can do for your network because there is a "Demo Mode" included with the Limited version that allows MU-MIMO to work for a run time of 30 days. So, you can see if you'll benefit from this feature prior to even having to pay for it!
If I turn the trial on for 10 days and turn it back off can I save the last 20 days of trial for later date?
Yes you can do that. It's a cumulative run time of 30 days.