Here are the solved grids:
I'm not gonna go through the whole solving process for the puzzles, but I basically used two techniques in addition to basic logic:
1. Cells touching smaller cages than the one they're in
Indeed, if a cell in a cage of size $n+1$ touch every cell of another cell of size $n$, then the number in the cell must be equal to $n+1$ to avoid any contradiction with the other cage. For example, this is very useful to start the puzzles:
And:
2. Finding cells that have the same number without knowing the number yet to get more information
A lot of times, you will want to use letters (or colors, or anything you like) to identify cells that have the same digit. It helps getting enough information for you to actually figure out what the digit is. Let's take the following example that occurs in the last puzzle:
By noticing each of the cells marked with an $x$ must be the same digit, we can see that $x$ must be between $1$ and $4$ (because of the 4-digit cage) and $4$ or $5$ (because of the green area), and therefore our $x$ is a $4$.
Applying these techniques with some process of elimination leaves us with the solved grids!