Hi Thunderchild,
there shouldn't be anything confusing about Maplin's.
Basically photoresist behaves like any film material (just being sensitive to UV-exposure).
I've made several thousands of PCBs using photoresist PCB material and no-name material is nothing to suggest because no result is repeatable.
Photoresist can be compared with any optical film. Assume you buy a 1,000ASA film and expose it correctly for it's ASA value it requires processing according to 1,000ASA (not 400ASA for instance).
The same applies to photoresist film. No-name products use different mixtures for the film and also undefined thickness (density), meaning you will have to test each PCB for correct exposure and development time.
Good brands use the same film viscosity and exactly the same film thickness (accurate to 1nm) ensuring the same result even when purchasing material at intervals.
Best results can be achieved purchasing PCB material at BUNGARD (Germany). Check out
Bungard Elektronik
To make top quality PCBs you shouldn't use a direct laser print on a transparency to expose the PCB. Make a 1:1 copy of the laser print using positive or negative film (according to etching method - direct etching or differential etching). For extraordinarily good print quality use repro camera equipment (available at book printer's - most of them are willing to help for some bottles of beer.
)
The copies have the same function as green TRF for the toner transfer method. Their pixel density is much higher than that of the laser, filling pure black areas purely black (instead of leaving small blind spots)
If the image on the PCB gets underetched the toner (film) is on the wrong side of the carrier. Even a transparency of 0.1mm thickness will allow to expose portions of the PCB caused by refraction, causing traces of <0.3mm to deminish while developing.
As a rule of thumb print the bottom side of a PCB the way you see it on screen (toner on top, which makes it have direct contact with the photoresist). Print top layers inverted for the same reason. (The toner must always have direct contact with the photoresist film.)
Hope that helps you for future projects.
Regards
Boncuk