It's tempting to buy an all-in-one curriculum and call it a day. It seems like a sure way to cover all bases and stick to the national curriculum. How else do you make sure you've covered all the topics? There are excellent all-in-one curriculums, but just like there isn't a car for every terrain there isn't a complete curriculum for every situation. What are the considerations?
Your child just may not be engaged with the materials. Perhaps they need something more hands-on or active rather than simple printouts or screens. Maybe their interest in math is much deeper than history. Perhaps the lecturer just doesn't speak in the way your student prefers.
Companies that specialize in producing materials for a single subject tend to do it better. It's the same principle as in school, where you don't really want one person teaching math, history, and biology. Larger companies that tackle many items at the same time just don't have the same focus as a specialized team. In an ideal world, one would find the best materials for each subject separately, but that's not realistic.
You may not change the study materials when your child needs it, because you've already paid so much money for this one amazing package. It's called the sunk-cost fallacy. You may not even notice. It may seem like your little student just isn't putting in enough effort (the materials are perfect after all), when in actuality they just don't fit with the particular teaching method. Just make sure your budget can fit adjustments in the curriculum if you do take the plunge.
In summary, all-in-one curriculums are not bad at all if you keep the above issues in mind. Mostly it comes down to being flexible and changing things up when your child is not quite getting the subject or doesn't seem to engage with these materials.
So what should you do instead? I've written about an effective way to put a curriculum together.