I use envelopeners a lot and indeed prefer them to any other means of cutting paper in almost all cases. Here are some tips from my experience:
Regarding the cutting tool itself:
First of all, envelopeners are consumables: they will become blunt over time and there's not much you can do about it. Since they are cheap, simply replace them once in a while, ...
I haven't used this tool, but I have used loose razor blades to cut paper. The "getting stuck" phenomenon just seems to happen sometimes.
I once grabbed a new blade that had a light coat of oil on it, and I had much better luck using it for a while. Assuming the oil had something to do with it, I sprayed the blade with some silicon lubricant and that also ...
That's not too big. You may be able to do it with an A3 rotary trimmer, if you cut the ends off first (A3 is 420×297 mm or 11.7×16.5 inches). These are normally slightly oversized (as is the example I linked), and may be sold under other names in places that don't use A-series paper, possibly with a different printed scale but the same ...
The simple DIY way
Use a ruler along the line to be cut. Use a cutter.
The more professional way
Use a paper guillotine.
The advantage of the ruler + cutter is that you can cut lines anywhere, anyhow, even holes. The guillotine will help you get cuts perpendicular to one edge, and the cuts must start at one edge of the sheet.
As many have described in the comments, there are a variety of computer-guided cutting machines, ranging from the cricket and silhouette level machines which are designed for home use, to more serious home-manufacturing devices like the silver bullet.
These devices differ from each other in terms of price, the size of media they can work with and the variety ...
A finger guard
Finger guards should go along the trimmer's base. It's a safety feature that prevents your fingers from being chopped.
A Tension Spring
This prevents a guillotine paper cutter from acting like an actual guillotine. The tension spring is attached to the blade so it won't move by itself.
A Blade Latch
It holds the blade in place when you aren't ...
I have not used this tool either but there are a couple of conclusions that should be easy to draw.
The tool is a fairly cheap one (in price not necessarily quality) so it would not be a stretch to think low quality steel or other metals might have been used. I would expect this to wear out and be more susceptible to damage then something like a craft ...