The OP asks ... would you be content for your party candidates to sign a loyalty to the leader clause ... The OP also asks us to answer the question regardless of party so I must assume the OP believes this applies to all parties in some way.
Firstly could I ask for some clarification from the OP and for some facts on this. As far as I am aware all MPs have to pledge allegiance to the Queen. I have seen no change to add Party leader's to this. What authority is asking all the Parties to do this? If so, which of the parties is compliant? What is happening to people standing as independents?
I have to say, in these days of fake news and false truth I do wonder if, in fact, any Party is asking this of their MPs. I am sure most people would agree that after the lies we heard during the referendum and seeing what is happening in America, where their leader's supporters can declare that it doesn't matter if a video is real or false as long as it gives the message they want to put out, we should all be assiduous in tracking down and identifying such fake news, false truth and pure propaganda.
I would want factual chapter and verse - a copy of what they have to sign and which Party is making their MPs do this before I even start to answer the OP.