budget diy cnc controller question

[m_c]

I'll answer the why are those controllers crap?
They use a very common, but failure prone stepper driver chip, especially if you try pushing them anywhere near thier limits. Which given the size of machine you're planning on building, you would have to do to get even moderate performance.
Individual leadshine drives (be that older M452s? or the newer digital drives) will allow for far more powerful motors, and far better performance. These cheap combined controllers/drives seem like a bargain, but when one of the axis goes pop, which they are renowned for, unless you're good with a soldering iron, the whole lot is junk. And you'll soon regret the purchase when watching your machine crawl doing rapids, as the drives just aren't capable of reliably moving it any quicker.