If you're new to the crack filling industry you've probably seen V-shaped and U-shaped squeegees. At the end of the day, they both do the exact same job but each has its own pros and cons.
V-shaped squeegees hold less volume of material within the tool, but because of the wide V shape, it can create a nice wide "band" on either side of the crack but this band can vary between 3" to 5", depending on how much material is in the squeegee area when you spread the material. This variance is great for different width cracks though.
U-shaped squeegees typically hold a little more volume of material but have a consistent banding width when spreading material. Each brand or model of u-squeegee you buy will have a slightly different banding width but most of them are around 4". These squeegees are usually limited to smaller cracks because you can't get proper banding if the crack is too wide.
So which one should you buy? For a lot of people, it simply comes down to personal preference because both types will get the job done.