The phone interviews were fine and the interviewer asked some technical questions. For the onsite interview, they requested to sign an NDA form that I did not follow up further with them. A professional company should perform interviews in an excellent manner and it should not expose candidates to confidential information. The candidates would be invited for the interviews as experts in their fields and if exposed to confidential information by accident or on purpose by the interviewees, their professional career can be damaged significantly in a close future. I do not recommend signing NDA with any company in the interview step unless you are sure that you would get a contract with a very high probability.