Promax diet is very good and Morba, no offence but you're comparing it to a COMPLETELY different product, i mean completely. Promax diet is fully suitable for a ketosis diet, the stuff you linked to is 1:1 protein to carbs, so its in no way a "diet" type meal replacement, it also has from a quick look nothing else in it, carbs have never and will never be expensive, thats life. Wether the stuff in promax is worth it or not is up to you really but, it has vitamin powder in, not expensive, but still an extra 10p a meal, its got CLA in, which most places is somewhere in the region of £15-20 for a 60 tablet bottle at 1gram a tablet, so thats an extra 30-40p for CLA in each serving, extra b-complex, and a bunch of other stuff, not particularly expensive, but you'll find it does help.
If I use promax diet(which I do now and then as its premade and just easy and quicker than making a shake with everything in it yourself) I DO notice the difference to having a plain protein shake. How can i know that, because the days I have plain protein shakes plus some multivits, b-complex I can feel the difference. is it surprising, no, why? When you're eating less food a day than a normal diet, and less vitamins and minerals but your body is trying to burn more fat, needing more raw materials as a catalyst to burn that energy somethings got to give.
Now theres no reason not to buy it all yourself and mix yourself shakes to a similar recipe, thats fine, but when you add everything up its NO DOUBT CHEAPER than maximuscle, but its MUCH closer than you think.
As for if you aren't exercising don't have promax, more crap tbh. Without exercise you still need protein, and losing weight you want protein, and less carbs and in a nice tasting shake with a good mix of other things is a very decent way to eat.
Its actually quite hard to follow a ketosis diet as, frankly so much food is carb based, after a few months I'm finding it harder to stay on the diet because I am rather bored, almost every meal I've eaten for the previous 20 years was mostly carbs, a quick easy shake that fills you up, is healthy and curbs hunger, can't see the problem myself.
Wanton, seriously, I guarentee you, losing weight is 97% diet, 3% exercise. you can lose weight without exercising VERY easily, you can not lose weight working out and eating crap, millions of people prove the later every day. Tonnes of people go to the gym to lose weight and get no where because they don't change their diet.
EDIT:- its also worth mentioning that like most sites they want you to buy in bulk. you get 4 for the price of 3, and fairly often they do the +25% extra free boxes. which means really its £32 a tub if you buy 4, and 99% of the other places you can buy it from will sell them for that price without buying in bulk. I think the cheapest I've seen it is £25 or so a tub on special offer though haven't seen it at that price in ages. I do hate the cost even when its cheaper, but frankly, if you stick to a ketosis diet and have a couple of these a day it makes life easier and has a really really good combination of things that help your body burn fat, its not nonsense science. Simple things, b-complex vits, not hard, sure you can take separately and cheaply, but its one less pill to remember to take and something that really does make a difference, as do the other vitamins, CLA's less proven but its still there and still costs money to add. With an "all in one" type thing its hard to say if everything works, only one thing, or the combination, but it really is a great MRP.
When I'm having a harder time I tend to buy a tub or two for an "easy" week, but cost does drive me away from it and I stick with unflavoured bulk whey from MP most of the time and make similar shakes in batches(which I stick in handily sized finished promax tubs). Every few weeks I'll make up a tub full of MRP's, mostly only protein with cocoa and sucralose sorted so I don't have to measure for each shake, and a preworkout carb + protein shake.