I have not bought or seen the Thames & Kosmos C3000, but I have recently set up a customized home chemistry lab like the one I had when I was a kid, and I base my rating (5 stars) for the C3000 on the list of equipment and the price. You should refer to other reviews for actual experience with this chemistry set; I am writing to share some of what I have learned in setting up my own home lab.
There is a lot of moaning on the internet about the way that fears of lawsuits and liability have led to the demise of the old-fashioned chemistry set, and about the poor quality and educational value of what typically passes nowadays for a "chemistry set". Many of these seem to be so "safe" that all excitement and learning has been drained out of them. See also the book "Uncle Tungsten" by Oliver Sacks. Some of the lesser Thames & Kosmos sets may fall into this category, and by the reviews I judge that they do. But the C3000 looks to me like it is a good start on recovering the experience offered by the classic Gilbert and Chemcraft chemistry sets of the 50's and 60's, especially in view of the price. While $212 might seem like a lot for a chemistry set, it is considerably less than you would pay if you ordered the same chemicals and pieces of equipment individually. Also, for those of you considering using this for home schooling, I would offer the opinion that it would be worth it to invest even more, and consider something like the $500 chemistry set offered by HMS Beagle, or by expanding on what is offered in the C3000 by purchasing extra supplies. The top-line Gilbert chemistry sets of the 1930's cost something like $40 (I think), which in inflated dollars must be more than $225 now. Besides, for home schooling you probably want something more than what any chemistry set offers.
There are some complaints that the C3000 doesn't have all the chemicals you will need to do all the experiments in their manual. I think that's inevitable, given the price. In any case, if you or your young chemists have any interest in the subject it is likely that you will want to expand beyond the limits of the C3000. I suggest that you get a copy of "The Golden Book of Chemistry Experiments" (out of print, but available as a pdf file for free download, just google on it). I also have the manual for the Gilbert Chemistry Set from the 1930's which has hundreds of experiments and lots of general information. These can give you ideas for experiments. Robert Bruce Thompson's book "Illustrated Guide to Home Chemistry Experiments" has a lot of up-to-date and useful information on setting up a lab, as well as a series of advanced high school or college level experiments. It covers topics such as safety and disposal of chemical waste that you will want to know about. I also recommend the videos by Nurdrage on youtube, which are very educational and interesting, although there are two instances where I wish he had restrained his language. Apart from that they are the best chemistry videos on Youtube.
As for ordering extra chemicals and equipment, I have used a combination of United Nuclear, HMS Beagle, Sargent-Welch, and Elemental Scientific. None of these covered all my needs, and I have shopped around. I started by concentrating on some particular experiments I wanted to do, and then ordering the equipment needed for those, and then moving on to new experiments.
Mineral acids (hydrochloric, sulfuric and nitric) and strong bases (sodium, potassium and concentrated ammonium hydroxide) are the main chemicals needed for serious chemistry that are omitted from chemistry sets (although the HMS Beagle advanced kit does include some of them). Companies such as Sargent-Welch will not ship these to individuals, only to schools or businesses. Robert Bruce Thompson explains how sodium hydroxide and sulfuric acid are currently available at the hardware store as drain cleaners, and also how to get hydrochloric acid. Nitric acid is the most difficult to obtain, but it may be available locally (for a price, that's how I got mine), or else try HMS Beagle. See also RBT's videos on Youtube on lab safety.