I fully understand that its cheaper to buy larger quantities of iron. The purpose of this post was specifically for those who only need a very small amount and do not want to store extra.
Are you sure you have an iron deficiency? Treating with iron is the first knee jerk reaction gottafixit after witnessing leaf chlorosis when the problem can be one or more micro deficiencies, especially zinc, even manganese.
Keyplex stuff is about as good as it gets for me.
The good thing about iron is that it is really tough to overdo it. Of all of the major, minor and micros, it is the only one that I know of that you really can't overdose on. May not solve your problem, but won't make it worse either. I'm a fan of foliage pro, looks deficient, hit it with foliage pro.