I'm getting good results on my serum ferritin blood tests while taking these Swanson Ferrochel iron pills.
Look up ferrous bis-glycinate chelate online and you will find reports saying that it's apparently gentler on the digestive system and better-absorbed (per mg) than the other types of iron available in tablets.
Also, Ferrochel's patent-holder Albion claims that this type of iron is not negatively affected by calcium (in foods or tablets), like other types of iron are. (Even the heme iron in meat is reportedly negatively affected by having over 40 mg of calcium at the same time, and it doesn't take much of a dairy product to reach that amount of calcium - few bites of yogurt, small amount of milk, little bit of cheese, etc.)
Swanson themselves don't give much information on this type of iron, but you can look at the patent holder's website for background information, some simple graphics showing the absorption process of Ferrochel, and a few medical studies on the formulation. You can look further afield by searching for studies of ferrous bis-glycinate chelate in the medical research articles offered on the pubmed database - there are quite a few that mention it. Additionally, I found a lot of good, non-technical information (in English) on the site of a Polish pharma company which uses Ferrochel in its iron formula.
If you are trying to increase your iron stores (which you should only try to do if you've seen a GP and made sure that's it is okay, because it can be seriously dangerous to self-medicate with iron if your body doesn't actually need it), please research into it and learn of all the foods that actually hinder iron absorption. You might want to adjust what you eat and drink, and when, if your iron store is very low and you are trying to increase it rapidly. Mainstream medical doctors don't get much nutrition education in medical school, so they may not be very aware of this kind of thing, and it's up to you to educate yourself.
One of the biggest hinderers (if that's a word!) of dietary iron in the UK diet is tea. Black or green, caffeinated or not, tea hinders between 60-90% of the iron a person ingests if the tea is drunk within 1 to 2 hours of eating a meal or taking an iron tablet. (It used to be thought that tea would not hinder the absorption of heme iron contained in meat, only the non-heme iron contained in beans, veggies, grains etc., but in a recent study, tea hindered 60% of the heme iron that was consumed along with the tea. If you are deficient in iron and trying to improve your iron status quickly, it's probably best to assume that tea is a no-no around any iron-containing foods, meat or not.)
Many other foods hinder iron in some way -- foods with phytates in them (grains, breads, cereals), foods with polyphenols in them (red wine, many fruits, some nuts, some spices, some herbs, some vegetables, some beans, chocolate, cocoa, many herbal teas like peppermint tea, herbal medications like milk thistle, turmeric/curcumin, ginkgo biloba, grape seed extract, and soy isoflavones), foods with phosphates in them (baking soda, carbonated soft drinks with phosphates, many packaged sliced meats, egg whites), foods with oxalates in them (spinach, rhubarb, beets, sweet potatoes, some herbs, some nuts), antacid medications, and other minerals like calcium and zinc can compete with iron for uptake in the digestive system.
Therefore, for the best chance of absorption, it's best to take supplemental iron at least 1 to 2 hours apart from any food intake, apart from most types of beverages (milk, teas, red wine, some fruit juices), and apart from any herbal medication or other nutritional supplements (like a one-a-day vitamin/mineral tablet).
If the iron in tablets upsets your tummy, as it does for many people, you can take it with some food, but try to choose something that won't compete with the iron (have a banana, for example, *instead of* a bowl of cereal or a few crackers or a few spoonfuls of yogurt).
Foods or tablets containing Vitamin C have been shown to dramatically increase iron absorption from supplemental iron, when taken together.
There is a lot of interesting research and medical advice out there on this subject. Researchers have a lot left to learn about iron, though. It's not as straightforward as it would seem.
Iron deficiency is widespread across the world, even in western, well-off societies like the US and UK. Studies have shown that at least 25% of women in the UK don't get enough iron in their daily diet, and apparently 8% of women in the UK have iron deficiency anemia (but many don't know it, because it's not something doctors here seem to routinely test for, and even if a patient is tested, the accepted minimum amount on the test is very low and there was an article in the British Medical Journal in the early 2000s saying that the minimum level should be raised significantly because a lot of women who are above the minimum score still have iron deficiency anemia and are not being treated for it because the lab paperwork says that they are in the "normal" range. By the way, that medical article from the BMJ is available to read without cost online.)