I made the same mistake when I bought Tesco's own meal replacement drink one day out shopping and found I was hungry. I opened it, drank it and only then decided to check out the information. It was something like 28 per cent sugars!!!! It's a minefield, I know, but diabetics have to read lables for sugars and carbs, which turn into sugars.
I was also wary initially of the sugar content but I worked out that the carb intake,
in terms of weight each meal, is low, so I decided to press ahead and see what happened. In the event, my BG has reduced substantially - it's now usually in the 5s and 4s - and my fasting levels are always < 6, sometimes below 5, and that was unheard of before I began the diet, when they were usually mid-7s or higher.
I settled on the Tesco 'Ultraslim' because of cost (it's only 33p per individual shake) and easy availability, but there are 2 formulations: The Strawberry and Banana and the Mango shakes have fewer carbs/ less sugar than others - 28.2% -v- 46.3% for the other flavours, and those are the 2 formulations I'm using.
Each sachet (i.e. one meal replacement) weighs 28g and contains 104 kcal (370 kcal /100g). It contains 28g x 28.8% = 8g of carbs (agreed, mostly sugar), to which must be added whatever carbs are contained in the liquid you use to mix the shake. I use 200 ml of semi-skimmed milk which I'm told contains 98 kcal, and make it up to whatever level I want with plain water. That gives me 202 kcal in all.
I'm not saying that the lack of adverse effects on BG that I'm seeing would be true for everyone, nor that there might be better replacement shakes out there. However, they seem to be working OK for me and, on that basis, I'm quite happy to stick with them.