I like flashbacks and flashforwards. Flashforwards are in particular, very cool for TLs.
I like them too when done properly. This timeline, unfortunately, did it too often and with poor execution, in my opinion. I originally thought that the first post was a "teaser" for 1968, and that the timeline would be mostly linear from then on (a concept which I rather liked).
In this timeline, however, the overuse of flashbacks and flashforwards led to two major drawbacks:
1.) It made the events much more difficult to follow, and
2.) It eliminated suspense. For example, after the initial post and the first few updates, we already knew:
A.)Nixon won in 1960.
B.)Kennedy defeated Nixon in 1964.
C.)Kennedy was involved in close reelection campaign against George Romney in 1968, and
D.)What the hot issues were in the 1968 campaign.
Most of the rest of the updates since then were only filler- we knew what the end results would be.
So, in conclusion, while I agree that flashbacks and flashforwards can be interesting to add to a timeline, the author must be judicious in their use.