DCA method isn't about safety but about the quantity of discretionary income at your disposal as an investor. If you've a large discretionary income available at the point you want to invest, then you can go ahead and lump sum and it's still financially safe. DCA provides a slow and steady approach to investing into Bitcoin and even when using DCA, if you're over aggressive in DCAing, you would not be too safe as you may not able to sustain it for long.
I feel that investing with lump sum is more recommended to those that have a steady cash flow, I can't advice anyone that does not have a steady cash flow to invest in lump even if he has enough discretionary income to buy in lump yet is not advisable especially to those newly investors.
You can have a steady cashflow and at the same time not have a large discretionary income at your disposal and I'm such a scenario the investor cannot lump sum since his discretionary income is limited. I'm lump summing, more emphasis is placed on availability of large discretionary income and not just about having a steady cashflow.