RE: to use a rubber or not to use a rubber
15 years ago I went with a peep. It worked but looking back it sucked. That extra piece is adding another component to a component ridden device that can fail. When I say fail I mean it can fail and you not know it. Just snag it on a branch walking through the woods. Don't damage it enough to show while your settling in you stand. Pull back and aim as the big boy is broadside at 15 yrds and hear twang. You get my point.
A kisser is just as effective without the extras hanging off. I use a red dot scope and love it but it does cost a little. I would never go back to the peep set up.
Good luck!