May be there are some different about this system.
I have study the line crossing system for quite some time. It has one advantage. That is price either higher than the line or lower than the line. So on pure math point of view this system can never loss.
Here is some draw back:
It has the problem of all crossing system,
1. one have to buy higher and sell lower.
2. Often time the price cross back forth many many times and all the trade entries end up lossers.
3. when news comes one may buy 100 pips above the line or sell 100 pips below the line according to entry rules.
to overcome the buy too high sell too low problem one can use price action to do the entry that is if bid/ask cross the line then make entry. But it will have many many back forth entries since price often cross round lines many many times.
to overcome too many back forth cross problem one can use short period MA cross line buy often buy too high and sell too low.
I'm sure these are very common problems that we all face in design a trading system not just line crossing systems.

In fact it doesn't matter too much where you draw the line. London open is only one excuse to make entry. The same problem is always there.