Pakaks Jalfrezi Paste is one of a range of different curry pastes made by Pataks. Pataks also make an extensive range of curry sauces. The biggest difference between the two is that a jar of paste is designed as a starting point for a meal rather than being used as a ready-to-eat complete cooking sauce. While you can use the pastes as a marinade you usually have to add either tinned tomatoes (Jalfrezi, Balti) or yoghurt (Korma, Tikka) in order to make a cooking sauce, as well as adding your own vegetables and meat, while a jar of cooking sauce only really requires you to add meat. For the lazy cook (read me as a student!) the cooking sauces are much less hassle to use, as well as being cheaper.
I live in Japan where Pataks isn't sold and its difficult to make decent curry. Whenever I visit home I put a jar of Pataks in the suitcase for the journey back. The reason I always choose the pastes over the sauces is because one jar will last for 3 - 4 meals depending on how frugal you are, whereas a sauce is only good for one meal. The pastes will also last a couple of months after opening too (mine do!).
Jalfrezi is my favorite type of curry. Pataks Jalfrezi has a grainy texture which tastes decent when mixed with tomato as part of a sauce, but to be honest I think the fully mixed sauces sold by Pataks taste better, and it doesn't stand up against a decent Indian restaurant. If I still lived in England I would probably not use the pastes, but us expatriates have to make do as best we can. One way where the Pataks pastes are more useful though is as a marinade. You can stir a tablespoonful in with some chicken and leave it overnight, and the next day it tastes great grilled or barbequed.
How I regularly cook with this -
One chicken breast
One courguette (if I can find one, pretty rare here in Japan)
A couple of mushrooms
Chop and fry all of the above.
Add two big tablespoons of the Jalfrezi sauce, fry a little more.
Add a tin of chopped tomatoes and simmer for half an hour or so.
Makes a good meal for two with rice. This is more or less the same as the recipe suggestion on the back of the jar. The jar also has instructions for how to marinade.
Overall, a decent product for the situation I'm in. Well worth the 1.85 I paid in Tescos, but if I lived in the UK I'm not sure I would use it much.