We use Sparx at school
I have found that it's brilliant, now that I'm confident with the teacher side of things.
I have found that those who are happy with it can thrive on it. The questions are written in an exam style, so they are getting students used to that - particularly those doing the higher tier.
Sparx has changed the bookcheck system so that you can move on now if you don't get the bookcheck right which will remove some frustrations hopefully. As a teacher I can see how pupils are doing on bookwork checks but you can still complete the work.
I get an email each week to check the topics that are to be tested in the next hw so I'm careful to check what is coming up and that we've covered it.
I regularly alter the level of the questions that my students are doing. So if a parent tells me that a student is really struggling with the content, or it is causing distress and frustration at home, then I will manually change the working at level from an automatic level (which is what Sparx decides you should be at)
If a student has struggled with a question many times then I get a purple flag on on hand in page, so I would then help a student in my class with it.
I think the way to deal with Sparx is to do work at it in 3x 20min sections,and not to sit and do it all in one go. I believe that Sparx aim is 100% in everything but I'm looking at the time spent on the task too. So if someone took an hour to get 80% then I'm not going to complain about the last 20%.
Sometimes from the other side you don't know what is possible for the teachers to do with Sparx and I know that some of my colleagues don't alter levels. I'm old school and part time though and absolutely do not want to go back to setting worksheets and chasing those up that we used to do it. I'd rather spent my time making sure my planning was spot on and using lesson time more productively.