I don't see any reason not to subscribe to ForeFlight as a new student. Like training in an advanced aircraft, the availability of the technology doesn't mean you have to use it's full capability.
Other than the location of the legend, there are only two differences between the charts on FF and the charts on paper:

1. So far, you can't write on the FF charts.
2. The FF charts depict your position on them

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I can see an issue with #1 in the learning process. You should learn how to plan a flight outside of FF and may want to have at least one local chart paper chart around for the purpose. But think of the learning value of being able to find mistakes when you transfer the flight plan for FF. Not being able to write on the charts (for those of us who like to) isn't an issue for students alone.

#2 is a non-issue. All you have to do is turn off "own ship" in the settings so that the little aircraft is not shown. You'd still have an idea of your position on the moving map but saying to avoid the iPad for that reason is sort of like saying to avoid the VOR in the airplane because it assists in your situational awareness.

There may even be learning benefits to an iPad. Consider, for example, sitting on the ground at home with weather taking place. Think of the educational benefit of being able to watch the FAA's weather products and the information they provide in real time, seeing for yourself the lag times that have caused problems during thunderstorm activity as thunder crashed nearby but the associated red doesn't show on the screen until some minutes later. Bingo - you've learned something experienced pilots don't know.

In short, in IMO, there is no difference between a student who learns with FF and one who doesn't. The quality of the educational experience depends on far more than weather or not you can tear the chart you are using.

That said, there is one consideration supporting delaying the purchase. There are bells and whistles you will not use in FF until you get or are pretty close to your private. Whether the cost/benefit makes the purchase worth it right now is a non-aviation question only you can answer. Personally, I'd probably wait unless I had other uses for the iPad.