I've been think about this a lot and will share some of my working thoughts about tissue culture plants in planted tanks. Part of my master's degree involved growing TC plants, but I'm fairly new to planted tanks. Also, the basics of TC are not that hard, but there's a lot of nuance that you can only get through more experience/a higher degree than I have.
TC plants are generally more sensitive than those grown out of culture because they have been babied their whole life and may lack some protective secondary compounds or anatomical features because there was no need for them in TC. They have adapted to the environment they are in and are saving resources by not building up defenses it doesn't need. But when you suddenly change this environment, it's a shock. They are also tiny plants, so they have less stored resources at their disposal to handle new stress.
In DSM they can dry out more quickly or succumb to fungal issues - basically the same problems you run into with potted plants, but worse. Similarly when they are submerged, they are can fail for any reason that new plants fail. If you don't have the conditions to grow a particular plant from a pot, you aren't going to have better luck with a TC plant.
One issue that is unique to tissue culture plants is that their growth is regulated by plant hormones (or synthetic versions) that are added to the media. Please don't freak out just because I said "hormones" - this is a totally normal part of the process. I'm going to glaze over the details here, but different hormones promote different types of growth and getting them balanced is a bit of an art because there are big variations between species and even individuals. When the balance is wrong you can get all sorts of weirdness, such as the C. parva I described that were all shoots and no roots and the HC that
@ahem talked about that didn't have a good idea of what was up and what was down. There are many different sort of abnormalities. As consumers, there's nothing we can do about this except to plant it as best we can and hope that it grows out of it. Some tough plants do and it's not a big deal, and others need to be carefully grown on different media types to create a plantlet with normal growth that is optimal for transitioning to the outside.
There are also TC cups where the plants are just in bad shape. The media isn't made to last forever, storage conditions can be dodgy, and cups can get contaminated. Anyone who knows anything about plants knows they shouldn't be yellow or brown or mushy.
There's one other issue that is hypothetical, but I feel it's worth mentioning. There are a lot of species available in TC cups and I wonder if they are all suited to be sold this way. Sometimes plants can be grown beautifully in TC, but just don't make the transition to ex vitro with a high success rate. I don't know if anything in the aquarium trade has that problem, but it seems possible.
I think TC plants could be a good way of saving money if they are successful, but I don't feel like it's easy to gauge the probability of success for most species. Carpeting plants may be the exception since TC and DSM have been used together for a while, but I have seen hardly any info on stem plants.
