You could always try them and if they make you constipated or otherwise unwell you have other options. It is true that liquid iron supplements are more slowly absorbed, but tablets are not. Ferrous sulphate is very cheap and that's why it is most commonly prescribed but it doesn't mean it is the most effective, and a lot of people are allergic to it as well because the sulphate part is very highly allergenic. Ferrous fumarate is an alternative that is apparently the most absorbed form of iron supplement available, in some cases though it can also cause constipation. I am not sure if its Asda or tesco but one of them sells the ferrous fumarate iron tabs for one or two pounds. You also have other 'organic' forms of iron derived from plants and herbs, these can also be very effective and do not tend to cause constipation, ferrous gluconate is one and there is another one that begins with b I think, something like bisglycinate (?) xx