Q: "I have a Chassidishe friend who I told about Techeiles. He told me that due to financial expense, he would choose Radzyner Techeiles over the murex, for the following reasons: 1. Breslovers, Radzyners and other Chassidim wear the Radzyner Techeiles based on the writings in Nitzutzei Shimshon, 2. He's seen other Rebbes wear Radzyner Techeiles in their Tallis Kottons, and 3. He felt that both are good as long as the issue with "Kala Ilan" is dishonesty in selling/wearing on and saying it's the other, which is one thing Radzyner Techeiles isn't accused of. My question to you is, do you consider it to be a sin if someone chooses to wear Radzyner Techeiles over murex, especially in light of the above? As both a Posek and Chassid?"
A: “It is the overwhelming consensus of Poskim Kadmonim that only Chilazon is kosher. The Radzyner Techailes isn’t from Chalazon, so it’s not kosher Techailes. I would give him some credit for perhaps intending to do a good thing, but he isn’t actually fulfilling the mitzva that way. It needs to be be Murex, which is the Chalazon.”
Q: “Pasul for Techeiles but he would still be fulfilling the mitzva of Tzitzis correct?”
A: “It would be Lavan. So it’s a kiyum of Lavan and a bitul mitzvas Techailes.”