Manufacturers recommended settings are only a guide & are generally meant for production type machines, the type of cut being made & the size will probably also be a factor I would think but couldn't say for sure, While the text you are cutting isn't tiny it is small enough to produce a lot of sudden jerky movements which can cause problems for a hobby machine such as yours because of it's lack of rigidity.
You would really be better doing some experimenting to find the speeds & feed rates that work best with your particular machine. you may well find that they are a lot slower than the manufacturers figures especially for text & graphics that are small
I don't think that particular Brand is available here in the UK but have machined a few other Brands like the Rowmark Adrian has mentioned, as well as sharp bits there are a few other things that need to be right for a successful result, your table needs to be completely flat & the spindle needs to be trammed to ensure it is square to the table along both Axis, hold down needs to be watched especially with the thinner materials as they tend to bow up in the centre when clamped around the edge, vacuum hold down is probably the best method but sticky tape methods work OK as well. Dust extraction has to be reasonable to prevent the cut chips welding themselves back on
My dust extraction isn't the best so when I am cutting materials like this I use an air line to blow the chips away, makes a bit of a mess but at least I get decent cuts