I personally feel that Libre is currently one of the best NMS solutions if you don’t have any budget for monitoring tools and your network is not of the hyperscale type. That being said, there are definitely feature and scaling limitations compared to commercial NMS products.
We are a specialized MSP and have used a single Libre server (along with other tools) for the past 2yrs to monitor our global network/server infrastructure consisting of between 500 - 1000 devices and 30k - 40k ports using the default 5-min polling. We run Libre on a big expensive AWS instance, and I feel like we are near the limit of what Libre can do on a single server setup at 5-min polling. While it’s possible to scale Libre by moving to a distributed setup, it also adds a lot of overall complexity that will require much more regular care and feeding then a single-server Libre setup. We would definitely need to move to a distributed setup if we wanted 1min polling in Libre.
Just to compare, one commercial NMS I’ve used in the past (Statseeker) was able to poll around 1million interfaces at 1-min intervals using a single beefy server. It licensing also cost tens of thousands of dollars /yr, so there’s your tradeoff.
In my opinion, Libre is not a good multi-tenant solution if you want to present monitoring data/alerts directly to customers. Libre has no concept of port groups, so for example you cannot create a group of all customer’s ports and limit access in this manner. Alert rules can get messy quickly too if you need to create lots of different alert rules for different customers. We monitor infrastructure for two different business units in our Libre instance and even with just this the monitoring rules are numerous and messy due to the different alerting requirements and devices of the two BUs.
Hope this helps you with your decision!