Having experience myself on DIY slotted disc and high performance brake pad on my previous car, I can say it is worth the money.
On my current car, I swap the stocks with some branded cross drilled disc and pad and also it worth the money.
Given any circumstances, they do provide me the bite that I need.
As long as you get yours done with a machine shop that really knows what they're doing (calculating the degree of angles and stuff), you are good to go.
Hairline cracks are common for cross drilled disc, especially when you're pushing the limits. Even stock OEM GT-R disc will suffer from cracks after quite sometime, especially for those track day enthusiast.