I was very tempted to get maybe the 7mm. I figure if I 2xbarlow the 9mm I have that should be good enough for me for a while.
A bit confused why you all need each one, all 4 ? Is there that much difference between the 7 and the 9mm ? or the 5 and 6, or 7mm ??
Just curious as I think one or two TMB's is good enough.
I use the 6,7,8,9mm TMB's with a Orion shorty 2x barlow or 1.5X if you unscrew the the lens off the barlow and screw it on to the eyepiece. (learned this on CN)
Gives you plenty of differant fl's and since the seeing is usually variable sometimes as little as 25X less or more power can make a differance as REC mentioned.