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. instead they should start from the DCA method so that to enable them get used to the market before they will start to figure out the strategy that can fit thier accumulation journey instead of starting with lump sum, DCA is the best strategy to start with then after you must have get to a point where you feel that the DCA is no longer working for you or maybe like a delay in your accumulation journey then you can decide to switch to lump or maybe to stick to the DCA method and be hoping to meet a buying opportunity to be more aggressive.