I think it would have been better to use a real hardphone at the time I was working at the company. Cisco never managed to work and IT was struggling with it. The UI was also terrible in my experience, the buttons didn't display so we have to guess if something was clickable or not. The window was also very small, I don't remember having the possibility to have it bigger, but if so, this would look terrible seeing at the very old interface.
As I have been working on Cisco VoIP PBX for the last 6 years, whenever there is any slackness, Cisco corrects it by bringing the next version of the product.
The only thing I believe can be improved is the log structure, while troubleshooting the issue, logs are a little cryptic, they take a little bit more time to go through.
All main features is very easy to access and use, only pressing a button or two (when you need to page up or page down the features set!) in the desk phone or a click of the mouse to place a call, start a chat, video call or a meeting. Very straight forward.
Cisco offers online instruction on the use of the VoIP but it has to be sought out. Likely, the do offer additional support but this is managed by our IT department so it is difficult to determine just how accessible Cisco has been regarding the implementation and ongoing support for this product.
Cisco has the most stable and reliable solution in our comparison with other vendors. The way Cisco handles the redundancy of the system makes our communications experience zero interruption problems, and that was very different from the other vendors we used before deciding to migrate to Cisco VoIP PBX. Another good point was the fast and easy implementation. Only two days were necessary to bring all systems up with all integrations we have (billing, AD, and MSFT Teams).
Can't provide the loved hard numbers regarding the ROI, but the flexibility from the business point of view regarding a rapid implementation of a new branch or even a headquarter, is a benefit that any solid company should aspire to have these days, and there aren't many options with these capabilities out there.