No disrespect but I have been using the BH Time Ranger for the last 2 years with a 1/4 to 1/8 adapter, along with a set of cheap ( but quality sound) Kensington headphones and I have had NO problems at all with the jack loosening , going bad ect.
To me, the size of the headphone jack is not an issue at all. I've been detecting about 14 years and most of those years I have used Tesoro and Whites with the 1/4, along with name brand headphones like, GreyGhost and Jolly Rodgers. These cheap ( I think I paid $3 ) on eBay have great sound and in the summer, I am not sweating my head off ( which is why I went this route). The only down side to these Kensingtons, is there is no volume control. For me though, with the Times Ranger, this is no problem at all and simply fixed with a separate 1/8' volume adapter.
Heres a link to the headphones. Apparently they have gone up in price in the last 2 years but they are rugged and VERY cool in the summer with great sound. http://shop.ebay.com/i.html?_nkw=kensington+33137+headphones&_sacat=0&_odkw=kensington+33137+headphones&_osacat=0&_trksid=p3286.c0.m270.l1313
NOTHING wrong with a 1/8 plug in my opinion!