Not sure about the Weider one but in my experience most of them are cheap productions. 9 times out of 10 I believe your better off making your own vs. buying in a store.
Most of the pullup/dip machines I've seen/used weren't balanced correctly and rocked when doing the pullups.
I went out and bought a fairly lengthy set of 4x4's (I think 12-15 feet is good depending on preference for height). Key thing here is you need to plant your posts at least 2 feet in ground for good stability. I just used quickcrete and let it set.
I drilled a good inch and a half hole in the upper part where I wanted my bar and then just bought a 4 foot section of pipe. It works pretty good.