How do those rabbis opposed to the RCA (“Rabbi Willig's”) prenup feel about the Nachlas Shiva document?

Question

Many American rabbis will refuse to perform a wedding unless the couple has a specialized prenup regarding halachic divorce. This is known as "The RCA prenup" or "Rabbi Willig's prenup." From what I understand, its mechanism is almost identical to one found in a document in Nachlas Shiva, from hundreds of years ago. Here's the quote from Nachlas Shiva:

ואם ח”ו שיעשה כמר פלוני הנ”ל לזוגתו מרת פלונית איזו דברים שאינה יכולה לסבול וצריכה לבית דין, אז תיכף ומיד יתן לה עשרה זהובים לפיזור מזונות. וכן יתן לה כל חודש וחודש משך ימי הקטט. וכל בגדיה ותכשיטיה השייכים לגופה. וירד עמה בדיני ישראל לבית דין שלהם, תוך שני שבועות אחר בקשתו ממנו, ועל פיהם יעמוד כל ריב וכל נגע.

Should, G-d forbid, Mr. so-and-so do anything that his wife, Mrs. so-and-so, cannot bear, and they shall need a rabbinic court, immediately he must provide her with ten gold coins for her support, and continue to do so monthly for the duration of the conflict ... The husband shall deal with a Jewish court following Jewish law, within two weeks of his wife's request to do so; this court shall have final say.

Yet I've heard that some rabbis are halachically opposed to today's prenup because they feel it's a problem of "get me'useh" (a Jewish divorce can be invalidated if it was done under duress, in some circumstances; here the duress would be the ongoing payments of support). Do they disagree with the above Nachlas Shiva text, or draw some distinction between it and the contemporary case?

Answer 1

If you can find where is the source (where in Nachalas Shiva) on hebrewbooks it would be helpful.

There is an old dispute whether Ones Mammon (forcing someone to give a get through money, in other words fining him if he doesn't gives a get) is considered an ones or not. The Rama says that there is an argument between the Bais Yosef in the name of the Mahari"k and the Rashba. The Rama says that lechatchila one should absolve the husband from the fine.

Here the situation is different, as the 10 gold coins could be pre-obligated as support (what he is obligated according to the ksuva and not connected to the get.)