As someone who is 2 weeks in in training 3 Digit system (Characters/Persons) in Memory League (Every game recalled in Compete) I find the biggest issue is finding the Vimages, as I might get lucky and get 68/80 one game, another 29/80.
So, the idea is that you could choose lets say 220-330 and practice these Vimages, if you notice that you are weak there. From 900-999 I am able to do ~1s each, and 000-099 there is many Vimages I do not find in time of a match.
-Memocamp has this feature
-There is flashing numbers on this site too. ( not convenient to use)
As Memory League is the best in terms of training, the graphics and such, which is why I and I believe many others preferes to train here.
It would be awesome to being able to Drill your Number systems on here!