You don't say the make but there are some important differences in operation. The main one is how the branches are fed in.
1. The slot is open and you just drop/push the branches through the slot.
They drop to the bottom where the blades chop them up.
2. The slot has a guide which takes hold of the branch and feeds it into
the schredder where it is choppped up. If for any reason the slot
becomes blocked you can turn the switch and the feed mechanism
goes into reverse and pushes the branche out again.
I have used both for myself and friends and the second one was in my opinion useless.
It is very very slow . The switch is inadequate for the job and burns out .
My shredder is the first method and has been regularly used for more than 15 years .
The other thing to mention is that shredders have evolved over the years and one big difference is the cutting blades . They use to cut the branches at right angles which as anyone knows who uses an axe is not an effective method, so now the blades cut by slicing at an angle . Which is much more efficient and less strain on the motor and its also quieter.