It all comes down to experience & trying as many different set ups as possible.
I 've 14 years of HA experience and I'm still experimenting , so could write a book on it
The Scout like the quark but unlike all other configurations has its BF to the front and
the etalon to the rear giving a 16mm window at the diagonal , it is a very convenient
package as is almost grab n go , however like the quark is quite seeing dependant , EP
selection , tuning and focusing are critical also.
If going down the Quark route then a 2" Baader 35nm filter is all the ERF you'll ever need
well up to 150mm and is much more effective than a standard ur/ir cut.
But for your first foray into the HA world it's hard to beat the PST ! a common
misconception is that it has a 5mm BF it's actually a 6mm and from memory only the
very first were 5mm (2004) , i 've had numerous PSTs and discussed them at length
but reckon that the best ever were from the beginning of the 2nd gen 2006/7.
In conclusion a modern second-hand one would be a great investment imho.
Brian