Hmm. I believe cotton burr compost can alter the pH of your mixture significantly, you may want to check up on that if you weren't aware. Also, I don't see how it would be of much value in "breaking up" the potting soil, unless it was screened first (with the mix using only the large particles). Even then, unless it becomes the major component of the mixture, I don't think it would be worth for the function of aeration.

It will never be my first choice, but Moisture Control does work. My initial perception was that it worked too well, even. I hardly ever water the many herbs I have in that soil, and have to convince myself that I shouldn't be sampling underneath the surface with a bamboo skewer. However, a plant like a tomato is often very sensitive to overwatering / anoxic soil conditions.

I don't have any tomatoes in the soil this year, but I do have zuchinnis and lots of herbs, like I said. I agree that the it does look very compacted at first... but over the long term, it seems to provide sufficient aeration for plants that are not too susceptible to problems related to overwatering and saturated soil. It has not noticeably compacted beyond the initial shrinkage (3 months ago).

The "aqua-coir" is theoretically able to absorb and hold the water within its fibers, but allow for air to fill in around it. It then releases it slowly, providing moist conditions - but not saturated, anoxic conditions. As far as I can tell, it works as advertised.. up to a point. I don't think its nearly as effective in protecting against overwatering as it is in protecting against underwatering. To have that extra moisture retention, you have to sacrifice some aeration. Dill, for example, did not do well in the soil - seemingly because of too much moisture. Chamomile and rosemary also underperformed, though I'm not sure of the reasons.

It can be unnerving when the soil of potted plants that are supposed to be very thirsty stay very moist for days, but it hasn't had an extreme adverse effect on my average plants so far. Whether or not it is able to stand up to decomposition over the course of the season remains to be seen.

Despite the success with other plants, my best guess is that tomatoes wouldn't perform optimally in it - there's just too many potential problems with tomatoes that are caused or compounded by too much water.

My personal opinion is that moisture crystals in a peat based soil is about as worthless as you can get... and I don't understand why anyone would take an already water retentive soil and add something that will make it retain even more moisture for a longer period of time.

Root systems require aeration for the exchange of oxygen and gases in order to be healthy.

Honestly, I think you'd be sacrificing healthy roots for the sake of convenience... and when roots aren't healthy, the plant isn't healthy and won't produce well.

It's really to the grower's advantage to water more often, meaning the soil is well draining and aerated and dries out in a relatively decent amount of time... very few plants like to remain saturated.

While I agree that watering more often is the better solution, it's not always practical - and often surpasses the amount of work people are willing to do for their plants. It's not ideal, but I don't think there's anything wrong with trying to make satisfactory gardening convenient for those who aren't as enthusiastic as some of us are.

The Miracle Gro Moisture Control Potting soil doesn't use "moisture crystals", it uses coconut coir and a wetting agent.

In theory, polymer crystals can actually prevent soil saturation/anoxic conditions by absorbing and holding the water internally, allowing air circulation around it. It slowly soaks up the excess water retained by the capillary pressure of the soil after bulk drainage is over, and releases it as the soil dries out. The expansion and contraction mechanically aerates the soil as well.