Hmm... I tested AstroJargon and wasn't having a problem. I'm wondering if you inadvertently changed something else. If you'd rather get a commercial focusing mask, here are a few options:
1) Gerd Neumann makes masks which screw onto the front of your lens just like a normal filter. They come in various filter thread diameters (just like normal filters) so you'd pick out the size for the lens you plan to use. This makes it a little less "universal". The downside is that they are rather expensive (I see the 77mm diameter mask priced at $109 USD). They are very well made -- not plastic. It seems to be machined out of metal which is then treated to make it flat black.
2) A MUCH more affordable option is the Farpoint "unmounted" Bahtinov focusing masks. It's "unmounted" because it's designed to fit on an existing camera filter (e.g. if you already have a clear filter or UV filter for your lens, you can buy this, it fits into the threads on the front of your filter and then you attach the filter to the camera lens. I'm checking OPTcorp.com and I see this mask (designed to fit into a 77mm diameter filter) is priced at $11.80 USD. But it is a little less "universal" in that they also come in sizes (to fit into your clear filter) which means you'd need to decide which lens you plan to use most often (of course at less than $12 you could probably afford to get a few of them for any lens you think you might want to use.)
3) A bit more "universal" is the SharpStar2 focusing mask by Lonely Speck (lonelyspeck.com). This mask slides into a filter holder such as a Lee filters holder or a Cokin filter holder. These are "square" filters that slide-in to the filter holder slots. Lee Filters makes holders in three sizes... 75mm, 100mm, and 150mm. Cokin makes filter holders in 67mm, 84mm, 100mm, and 130mm wide slots. 67mm is really intended for use with point & shoot cameras. The 84 and 100mm sizes are designed for use with DSLR cameras (with 100mm being the most common AND it's the one size which is common between both Cokin and Lee Filter systems.) The holders on both systems require that you get an adapter ring (they're cheap) designed to fit the thread diameter of your lens (it snaps into the filter holder so that the filter holder will mount to your lens.) I bought the 100mm width SharpStar2 and it slides in my Lee filter holder. Due to the way it mounts, I could attach it to any lens that has filter threads on the front (the most I'd have to do is buy another adapter ring -- but those are cheap.) The price wasn't bad... $69 USD for the 100mm size. Incidentally, this filter is "clear" (unless most Bahtinov masks which are solid black with clear "slots" cut into them) and it's etched to throw the diffraction spikes. The upside of this is that more light is passed (a typical Bahtinov mask probably blocks about half the light -- so you really do need a bright star to focus.)
As with all Bahtinov focusing masks, you need a bright star and it must be a star (not a planet) -- don't attempt to use it to focus on, say Jupiter for example. The diffraction spikes won't be tight if you do that and it will be difficult to see if the spikes converge at a common center point. But the good news with focusing objects in space is that if ANY object is focused, then EVERY object is focused. So pick any bright star, focus, and then re-point the camera to the section of the sky you want to image.
I was never _really_ able to achieve good focus until I started using a focusing mask. I always just got pretty close, but could tell the stars were all just a touch soft.