Just wanted to throw out, for people lurking, that it is VERY hard to control what you eat while you are low or feeling low because it does affect your cognition (reasoning and judgment) and a lot of the chemical messages being sent are of a very primal nature, i.e. eat now or die! So I think it's more productive to do what you're doing, Remmer - look at ways to externally restrict the amount of carb one is likely to eat, by using prepackaged foods and things with easy-to-determine portion sizes. As opposed to trying to "get" the person to have more self-control while low.
Another thing to remember is that BGs are more likely to be erratic after a low, even an appropriately treated one, than they would have been without one. A low sets in motion certain chemical responses in the body that can affect BGs for some time afterwards, particularly if the liver gets involved. Unfortunately from the outside we don't have any good way to know if the liver has gotten involved or not, so we have to always assume that it might have. A liver dump can cause a high BG following the low, even if the person treated with only the minimum carbs necessary. And it may lead to more low BGs in the hours that follow, particularly if the person tries to correct for the original liver dump high with insulin.
Two things follow from this; one is that it's important not to jump straight to pointing the finger at overtreating just because a person has a high BG following a low - the body after a low is an unstable environment for up to 24 hours after the fact. The second is that unless you are 110% sure that a high BG after a low one is down to overtreating (like, okay, if I've eaten three tortillas, five spoons of peanut butter, two apples and a Pop Tart and am now at 21.something it's probably safe to correct a little, lol!) it shouldn't be corrected for at all and if you ARE going to correct a post-low high you should work out what you would normally give and then only give about half that.
What people use to treat lows is down to personal choice, what are you looking for - speed of digestion, degree of perishability, degree of portability, taste/texture questions, etc. For me I want my hypo remedy to fit in a pocket (so I can go for a walk without carrying a bag), not be affected by heat or cold, relatively long shelf life so I don't have to replace it if I don't need it for a long time, and to be palatable but ideally not taste SO good that I will be tempted to eat it just because. Kind of a tall order! I gravitate towards pre-packaged fruit leather, but I've been told such a thing is less available in the UK. Here in Canada it's called Fruit-To-Go and it's just about perfect. Before that I used to use those little fun-sized boxes of raisins but they don't exactly have a slim profile. I do also use Dextabs (but I find the tubes are so large that fitting them in a small bag or pocket is tricky). I've tried the hypo gels and found them disgusting (others swear by them though so don't go just by me!) I don't like liquids because then you have to carry the bottle around plus it's hard to dose out. But if I'm out and about and find I'm low, it's fine stopping in a shop to get a Coke or a juice or something!
I think from my own experience and from others I've heard on the forum that slow carb is overhyped for treating hypos. But it all depends on the situation, too - how much insulin is still on board, is there activity coming up, how far away is the next meal (or the last one!), do you often have hypos that are difficult to treat and require lots of carb or are you more likely to just need a little carb "top-up" to correct minor wobbles? So the official advice is 15g/15 min., repeat as needed and follow up with slow carb, and that will definitely keep you safe in all situations, i.e. you can't go wrong with it in terms of treating the low. However in terms of maintaining appropriate levels after the low, it isn't always what is necessary in a given situation and can sometimes be overkill. It's really down to how good the person is at noticing their lows (if there is a chance you might not notice that you are still hypo/hypo again and need to re-treat, best to err on the side of caution), and at sizing up their situation and knowing what their body is typically like (including whether it's unpredictable and not "typically like" anything much) to figure out what exactly is needed.