I agree, Stobart has the same RVR limits as other operators into the Isle of Man, Cumbrianboy is spot on the mark with his comments.
New ATR - 600 series aircraft with clearvision (EVS) technology installed would have a slight advantage over other aircraft however the runway lighting is still an issue. CAT II is really the only option.
Flybe/Stobart really do try their best to "get in" by carrying plenty of holding fuel and sometimes it pays off. Can't say the same for Easyjet.
The other issue is crosswind. This is where I have to admit Stobart is a bit restricted in their operations, no circling in IOM as of yet. Having said that, this is rarely an issue compared with the fog.
And in defence of ATR, the latest versions are extremely capable aircraft. EVS, PBN, STOL version (42-600S), Hot/High (Boost option), high density version (78 seats), combi version, front and/or rear door option. For pax, large stand up cabin, greater seat pitch/width, large overhead bins, very quiet, Wifi connectivity etc. Overall good reliability with minimal ground support required.
The "lack" of power is actually the selling point for ATR, extremely economical aircraft with good field performance carrying at least 70 pax. The slower cruising speed makes minimal difference on short routes up to about 300nm which is what it's designed for. It simply is the best aircraft for the job and the orders show.
Just one thing I'd change though, an APU instead of Hotel Mode !!!!!!!!!!