No, if you're wanting help with the formal logic elements of the 1A logic paper, then read the Smith book. Peter Smith is the examiner who sets the questions, and he is also the lecturer. It makes sense to read and work from his book.
Personally, I don't see how any introductory formal logic book could be better. It's clear, easy to follow, and doesn't shy away from demonstrating the proofs where they're necessary. What more do you need?
re: how hard it is, some people find it very easy and some people find it very hard. This doesn't seem to relate much to how good they are at philosophy. You can pretty much avoid ever having to work with it, though. There is one compulsory "formal" question on the 1A Logic paper, but that will normally include questions on set theory and probability as well as QL translation and logic trees. Personally, I found the worksheets a nice change from reading and writing essays, but I should be a mathmo really.