This is what I use. It's extremely easy to line up the cutting blade with the edge of the cover to get a perfect cut. The blades can be easily replaced. There is also a strip underneath the cutting blade that can be replaced over time. This strip helps with guiding the blade and providing a clean cut completely through the paper. They sell a scoring blade for this cutter, but I haven't used it. I purchased mine at Michaels. I don't remember the price, but it was reasonable and it's pretty easy to get 20 to 40% off coupons there. They also sell the replacement parts.
The best advice I can give is this. If the cutting blade doesn't line up perfectly flush with the straight edge, DO NOT WASTE YOUR MONEY. Many paper cutters are setup this way making it extremely difficult to get a perfect cut along the edge of your cover.
