That's just the opinion of one person (the owner of bitmixer.io). Granted, if you can find a better way around not using them, I'd suggest you go for that other way instead.
If Zcash is one of those coins that have it so that the output is spent from a hash of the input address that it is difficult to fin the input address but you can find the input transaction then that might be a good thing to convert to. I'd suggest trying a service like shapeshift.io once you get the bitcoins as you can use that anonymously (with tor) and they're quite reliable (for when I've used them anyway) - the rate is not as favourable but it is instant and requires no account to be created. (Though I'm not sure that Zcash is accepted there)
so what if
one of that bitcoin mixers is getting busted for money laundering or other rightfull reason... (we've seen that many times with the marketplaces, TOR is not the panacea until there is a human factor). aren't all associated wallets getting compromissed then?
..
also,
http://zerocash-project.org/how_zerocash_worksIt would be pretty difficult to get the identity of a mixing service if it goes through tor and/or cloudflare, not impossible but difficult nonetheless. Also many countries consider it to be in ethical to do money laundering and not illegal. Also, mixers are mainly for anonymizing coins in the same way as cash does.
With tor, it is advisable that you use some sort of paid for von and is hosted in a country where the government will never demand logs of the information transmitted. I think most operating systems have an option to use multiple vpns at the same time as well, before you even enter tor.
Also, tor isn't that secure really as a full route of your packets can be detected by your computer so it will be known to the other nodes as well (and SSL isn't that great as it's normally only 256bits and given every website includes things in HTML like <body> <head>... it's easy to crack if you have all of the packets).
