Yes if money is an issue then that is undeniebly neccessary. Your mentor is first to impart knowledge and skills to you as well as help protect your investment. If you refuse to supply the tools to do that with then yes you will likely loose this airplane not to far into your training.

If your mentor does not care if you use a buddy box then you have made an exceedingly poor choice in instructors and this is going to be a very expensive process.

That airplane looks to be a reasonable large trainer with a small gasser. I have mentored several in past years with a similar big trainers from Joe Bridi. What you must realise for example is how much does those props cost, I know but bet you don't and I can imagine what you are gonna say on your first prop strike and the next and the next. When normal trainers the props are a couple of bucks apeice.

This is a very expensive route you have choosen even with cheaper fuel and you need to be aware of that fact; Yup you can do it but key to your dreams will be the right instructor and much more money than if you went the normal stages with a typical trainer.

This seemingly irrational hate of glow powered aircraft that you profess to will close off an entire world of wonderful flying adventures and airplanes, thats sad.

John