Hi,
I use the photo-resist board for my homemade PCBs and get excellent results.
I've been using some photo-resist board which I first bought about 6 to 8 years ago, so my times are all a bit odd, I'm sure, but then I'm surprised it works at all! I have just bought some new photo-resist board, so I'm sure some times, like the developing time, will come right down.
I print my circuit tracks on transparency sheets with my Epson Stylus 740 inkjet printer, with it set to photo paper/glossy paper, highest resolution. This means more ink is put on the transparency, so it's nice, thick, and dark. I print the same circuit three times separately, and then dry them with a hairdryer as the ink stays smudgy for ages otherwise. Then I tape the three together, ensuring by this that no UV will penetrate to a large enough extent to expose tracks.
Then I place the transparency bundle on the board, place a piece of glass from a photo frame on top, place my wife's UV face tanner over it 3 inches from the board, resting either end of the tanner on the can tops from my isopropyl can and freezer spray can, and expose for 12 to 15 minutes.
I then fill a tray with my sodium-metasilicate developer solution (I think they call this carbonate-based) and - maybe only as it's old board - have to leave it in there for 15 minutes. I swirl it about every now and then, ensure that all photo-resist has come off where it should do, and that the tracks are clearly visible, then remove and wash with water.
I stick the board in hot ferric chloride (I warm mine in a jug in the microwave
) and agitate it the whole time it's etching (until I finish building my bubble etch tank) which speeds it up. Takes from 20 to 30 minutes to etch fully.
Results are spectacular. Most professional looking. I used to use the sun to expose the boards back when I first bought the 6-8 year old boards which I still have. Results were highly variable and never as good as now, since I started using the face tanner.
I only had the speckled finish when using normal copper-clad boards and etch-resist pen. Maybe you're over-exposing the board or, from what it sounds like, your print on the transparency (acetate) is too thin, or speckled itself, in the way ink usually is when on a shiny surface. Do what I do with the layers of transparencies (remember highest resolution for more ink) to make the tracks uniform in texture and very dark.
Hope this helps.
Now, I've got to try and work out why a laser printer I've been given is printing faintly in some areas every now and then, cos I only wanted it for printing my circuits on transparency in the hope that I could print just one and that'd be opaque enough to stop the UV, instead of printing it three times and overlaying them. Sadly, even where it doesn't fail to print properly, it still seems very thin and holding it up to the light shows how transparent it is. More so than one print from the inkjet printer! So much for my belief that a nice thick layer of plastic toner stuff would be placed on the transparency...