Also my tax consultant recommended it because he thinks it is important that the tax logic is certified by an experienced company (KPMG).
This still isn't enough. I would much rather hire a CPA to handle this issue, instead of putting it through a computer program and praying that everything worked out correctly.
Hire a professional CPA who knows (or is familiar) with cryptocurrencies and the laws surrounding the capital gains around them. Don't use a computer program because it's much cheaper.
I am very sure that no tax consultant will do the tax calculations without a program. Nowadays, the tax consultant programs are unfortunately not made for crypto currencies. No tax consultant can calculate with FiFo or transactions on different stock exchanges etc. without a professional program.
And because you said you shouldn't use it just for being cheaper: If your tax consultant's fee exceeds your profit, it makes no sense for me to hire the tax consultant.
Most of the community of crypto currencies all reject the old values like FIAT money etc. but with digital innovations like tax programs that can replace tax consultants everyone is afraid...
Oh I'm not saying that these tax consultants aren't going to be using programs as well, they are. But they're going to have the knowledge to look at what the program spit back at you and judge if it correct based on their prior understanding of capital gain / tax law.
I'd rather be safe than sorry when it comes to taxes, so I wouldn't want to trust some online program without seeking out a tax professional (CPA, in the states)