What learning type are you?
During my studies I realized that the possibility to customize learning settings is really one of the most important aspects for them to be effective. I personally prefer written and visual information to auditive only information because I am much better at processing written/visual information. Another aspect that I find really important - and I realized this while using an online platform for learning Spanish that did not have this function - is the possibility to "take a step back" in your learning material, i.e. being able to look at lessons (e.g. grammatical rules) that you have learned before and that you want to refresh.