Good morning Tyro.
I will try and help and keep it all rather simple
AND general, trying to keep things simple and fairly short.
I believe that that is no reason to own a single handed fly rod SHFR.
Because they limit the caster to where they can fish/cast.
Because the require a greater skill to master than using a fly rod with two hands.
The above two points are the key to why people should use a Switch rod or Double Handed rod, be is a beauitful flowing Spey type or an aggressive Overhead casting type.
Sadly today’s SHFR is being built faster and faster, the action, which then requires a better and better, higher and higher level of caster skill.
This then reduces the rod’s possible performance with Spey type casts, which are ideal for tight locations be it in the salt or the sweetwater.
The rod then is ideal for overhead casts only, this sole factor then reduces the time the angler’s fly is on or in the water because of the time consumed by overhead casting where as simple roll casting takes about one quarter of the time to complete or LESS.
The fast overhead casting SHFR then is unsuitable for tight location fishing where a Spey or roll cast would open up another World to the fly caster.
The very same World where the spin fisher thinks as normal, simply because he or she does not require any space for a back cast.
However the caster, in most cases is not increasing his or her skill levels and as a result the SHFR in almost all cases can perform far better than the caster can extract from his chosen casting tool.
Enter the Switch rod. SR
This is not a new concept.
BandW from Britain built these forms of fly rods years ago, and now some years later the World is suddenly discovering this brilliant and highly talented… (yes brilliant is that) form of casting tool.
Why the new discovery, simply because of marketing, and Companies wishing to sell the consumer another product.
To me and others (not all of course) believe that Swich rods are the perfect answer to the thinking, fishing fly caster, be it salt or sweetwater, because now there is a rocks that can be driven by one hand if the angler wishes to do so in overhead casting, where there is space, clearence behind the caster or where the location has trees or rocks and or other problems behind the caster that stop a overhead cast being complete, then the two hands holding the rod allow the rod to be driven into a Spey or simple roll cast with complete ease.
Ideally the SR should be in the 10foot plus range length to enable ‘better’ Spey type and roll casts.
However the above even a 8fot SR will produce far better Spey and or roll casts because the caster now has two hands to rotate the rod with a clearer snap action at the end.
opp, sorry I could write a book on the subject… 
Trust the input has not confused anyone.
Kind regards,
UB
ps, Tyron, you will notice in the future, the anti two hand fly rod users are the people who have not fished in real life situations and do not understand the value of being able to fish where most cannot, against trees, rocks or weeds behind the caster or under bridges. (I love under bridges in the shade in the middle of the day.)
Which is strange because I’ve found in the locations where 99.9% cannot cast/reach in their cast is where most fish live and do not appear to be as shy !
We can talk about suitable line shapes for SR’s some other time, maybe.