Oh wow, I didn't know they had an RSPCA there. Cool. Too bad they are underfunded yes. I used to work at a humane society that was exactly that, and it was quiet scarey there, to work and for the animals living there.
If you adopt a cat from them, have you thought about seting up a vet appointment PRIOR to adopting the cat? So as soon as you adopt kitty, your straight off to the vet from the RSPCA. So when you bring the cat home you will know if he/she has anything or not and you can adiquitly place the cat then (aka in quaranteen.)
Or are you saying they don't even have the money to test ahead of time for things like FIP or FLV? That could be a problem if you have kits in the home already.
As far as the foods. I'm taking a quick glance at them. I personally perfer cat foods with NO corn what so ever, but Eagle Pack and Royal Canine have it. Royal Canine does have a leg up, in the order of the ingredients, Corn is #3 and #5 in the list of ingridents. On Eagel Pack it is #3 and #4 followed by Chicken FAT, instead of a better ingredient like Chicken that Royal Canine has. The first 5 ingredients in a bag of dry food are often the most important to look at, if your going for high grade foods and in what quanities (prior to cooking).
You can see what I mean here, and decide for yourself, what to feed next, but I will say that yes Royal Canine would be better then your current diet.
Protein: 32.00 %
Fat: 20.00 %
Chicken Meal, Ground Brown Rice, Corn Gluten Meal, Ground Corn, Chicken Fat, Chicken, Flaxseed, Brewers Dried Yeast, Poultry Liver Dogest, Wheat Germ Meal, Dried Egg Product, Pork Meal, Fish Meal, Alfalfa Meal, Tomato Pomace, Drid Beet Pulp, Salt, Chicory Root, Dried Cranberry Powder, plus essential vitamins and minerals.
Crude Protein: 32.00%
Crude Fat: 13.00% <---- This is also a good thing!
Chicken meal, brewers rice, corn gluten meal, chicken, corn, chicken fat (preserved with mixed tocopherols), pea fiber, beet pulp, chicken flavor, powdered cellulose, fish oil, dried egg products, brewers yeast, sodium bisulfate, potassium chloride, calcium carbonate, choline chloride, DL-methionine, taurine, natural antioxidant, iron proteinate, vitamin A acetate, vitamin D3 supplement, vitamin E supplement, zinc oxide, zinc proteinate, ferrous sulfate, manganese oxide, calcium pantothenate, manganese proteinate, niacin supplement, copper sulfate, riboflavin supplement, pyridoxine hydrochloride, thiamine mononitrate, copper proteinate, calcium iodate, folic acid, biotin, sodium selenite, vitamin B12 supplement.