Most important. I am immediately available to my customers. I do not waste time with transportation and this is also cheaper for my customers.
When I am in the office and working on a PC, I use the ISL for Windows operating system. I use ISL on my Android operating system outside the office. Both of them work perfectly, even when I use the internet in roaming. Data usage is low.
ISL is by far the easiest for the user. I tried a few other systems, but I've always met the questions "how to proceed" and "what do we have to do", "where do you say that I find the right button" ...
In short. I'm satisfied with the ISL.