Have been using a DS4 for 18yrs for rec diving and everything is fine. I also have a DST but only use it as dec tank and do not find the 5th port has any use in rec dive. However, DST has 2 HP ports which would be useful if you want to run a spg and a transmitter..
As far as I am concern, the FST(100) sits in a no man land once FSR(200) made its appearance. The FSR is the only model comes with an replaceable valve seat and the latest model is also compatible to the 5th port.
The adjusting screw on the 2nd stage is nice but doesn't worth the extra US$110.00. DIY if you can source the part. Unfortunately, you might find it difficult nowadays even in Europe eg. Scuba spare will no longer sell you apeks spare unless you are a registered Apeks technician!!!!!! Anyone know a reputable Apeks spare parts supplier? Please send me a pm. Much appreciated.
Good point with the 2 HP ports on the DST/FST/FSR. I was actually thinking about pairing my Suunto with a transmiter in the future... But I would like to keep a spg just in case...
---------- Post added August 5th, 2015 at 09:51 AM ----------
Thanks guys,
The XTX50+DS4 looks like a good solution, however I wasn't able to find a better deal than this one I'm looking at with the XTX100+FST... Just USD 450 or so...So, I think I'm gonna go with the XTX100