I only have about 16 hours on my 7500, but here's my input.
I haven't taken the FEL off yet and I mow with a RFM. manuevering around trees has become second nature and the FEL has gotten its share of use. I was glad it was already hooked up. I did some major tree trimming (so I could leave the ROPS up when I mowed) and tied the branches together to drag them back to the rear of my property. After I threw the second pile onto the first pile which was already tied on, the front end got real light when I went to drag the whole works. I just put some cement blocks in the FEL for makeshift balast and the front end stayed down fine, even on a slight grade. It was also handy for carrying my chain saw while doing the cutting and for standing on to get up higher. (Don't tell OSHA /w3tcompact/icons/smile.gif)
I also used the FEL in an emergency to scrape down a temporary road over my creek that high water was running around rather than through the pipe. I then dumped a dozen loads of gravel to dam/divert the water back into the creek. Prior to this, there was a new creek running beside my house and towards the neighbors house because the water couldn't find its way back where it had come from. I guess I'm saying, if your going to buy it thinking you might use it, leave it on. It might have more uses than you planned for.
My rear tires aren't loaded and the RFM kept things very stable when I was moving full loads of wet gravel. I'm not sure how the weight compares to a box blade.
Good luck,
Fred