is debit card safe to use for top-up my account?

[Free Gift]

Help

[Doc Roley]

It works....I have to say I have found it problematic, I think you are better off buying 'Steam gift cards' with a particular dollar value from a game shop like 'EB games' (or your equivalent).
The reason I advise this approach is that the last 2 times I used my debit card steam banned me for 2 -3 weeks from the community market for ' using a card not usually associated with my account' (not the exact wording but that was the gist of the message).
This was nonsense as it was the same card I always used on steam but whatever.
TLDR much easier to just purchase gift cards & redeem online in my case, your mileage my vary.

[Cathulhu]

As safe/unsafe as any other payment method.
I'm using Direct Debit since i have a Steam account.

[Supafly]

Debit, Credit cards are fine along with Paypal and other methods. If doing it inside the client data is encrypted. If you do it via a web browser make sure the page begins with https not http when you enter details. The S is for secure meaning the traffic is encrypted, this goes for any online transaction.

EDIT: I would make sure the Save payment info is not checked. Makes life easier when you change cards, it expires or you change bank. Plus if your account happens to get compromised they can't buy and gift games using your saved payment details.