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 in such a scenario the investor cannot lump sum since his discretionary income is limited.
In lump summing, more emphasis is placed on availability of large discretionary income and not just about having a steady cashflow.
I don’t think it’s necessary for you to lump sum, when you know full well that you don’t have enough discretionary income, DCA is quite an efficient strategy in this situation that is why it’s more advisable to choose a specific strategy that could absolutely work out for you, if you have a steady cashflow and you end up not having enough discretionary income, then I will advise you look into your expenditure and your weekly or daily expenses and try working on them, and also adjust where you feel you can adjust to your expenses accordingly.
However when you want to lump sum, you should quite look carefully if you have the amount of discretionary income to appreciate lump summing, either way if you feel uncomfortable you could actually do a little more by buying a DCA, which could be more affordable for most newbies and beginners, some folks even have the ability to lump sum but still choose to go tremendously over with DCA because they feel comfortable with it.