On the cornet thing. Many cornets can have a trumpet like sound, while some are decidely softer and mellower. The line between differing sound on some of these horns is sometimes little or nothing at all from a trumpet. I have owned many cornets, from a Conn 80a to a Bach Shepards crook, to a Martin Committee, to name just a few. All 3 have very different tonal qualities, with the Martin having the most trumpet like tone of the 3. Tonal qualities vary with the players input as well. If I want to sound as shrill and strident as a trumpet, I can do so quite easily on many a cornet. Most of it comes down to the desired effect. Cornets are usually the choice for a softer sound, but I have heard some great trumpet players laying down some "butta". Again, it usually comes down to the guy at the end of the horn.
As for lending horns. I deal with that on a 1 to 1 basis. I have known many players that I wouldn't lend my used chewing gum. And on the other hand, I have known many people I would lend anything. Most of these people would NEVER ask to borrow something, which is why I trust them so implicitly. A perfect example is my friends who recently gave back my YTS62 that I had lent to their son. After much coaxing, they agreed to allow their son to use the horn. This came about because they had purchased a poorly treated Conn 16M, and after much frustration on the boys behalf trying to play on this abused 16m, I could no longer bear to watch it. I dearly wanted this boy to have a decent horn to play. I knew that if anything happened to the horn, they would make it right. I also knew their son would take good care of it, and he did. He used the horn for his entire senior year of high school, and advanced to 1st chair with their jazz program. I knew he had it in him, he just needed a little help, or better yet, less of a handicap. I really don't know if his enthusiasm would of overcame that 16m, and allow him to flourish as he did. It also helped to show my friends the need for a quality horn, even for a beginner. I just helped them purchase a Yamaha Allegro alto for their younger son. He now has a horn that will serve him well for many a year.
Would I lend a horn, you're damn right I would, maybe. =)