Here are my tips.
Make sure you get "clean" data from your old site. I am transforming and cleaning XML and HTML to get it to the point where it is a well structured Excel file. This will vary based on your data. For me, this is where I spent the majority of my time. HTML encoding some things, find and replace other things, it is a pain.
But, once you have clean data, you can use this extension to import into Joomla as regular articles or K2 items. I ended up using K2 so I could structure the content better. That is very powerful, so I highly recommend looking into that.
Take your time to make sure you set up everything first, and once you finally have everything set up, you can easily move hundreds or thousands of items in no time.
I would much rather go through the time and trouble of setting up all of this (getting old data cleaned, setting up this component to prep it for data), then to do some other manual copy and paste process. It did take me longer to prep everything than I thought, but most of that was on the old CMS, and my own learning curve for K2 and this extension. But, once I got everything figured out, this extension really worked great.
I did have to save my Excel file to the older XLS format, that made the data load better into Joomla for some reason. Other than that, this extension worked great and was consistent and predictable. I highly recommend it if you are going to migrate from one CMS to Joomla. The K2 integration was key for me, and I suggest you consider that if your data is anything more than plain.