From an electronic standpoint, they are similar to the regular 2600 joystics that we all know and love. The Junior sticks, obviously, don't have the plastic insert, so you don't have to worry about it breaking. The only other difference is the arrangement of the contact switches. Directionally, they are backwards compared to the older sticks.
***Edit for clarity of thought***
You asked about the junior sticks and I went off on a 7800 tangent. Never answer in forum when you are seriously sleep-deprived.
The only diff in the junior sticks is that they were newer.
. . .going to bed, now