There seems to have been some changes at USO as far as the the custom options are concerned. In their 2014 lierature it looks like they have discontinued a few scopes and significantly limited the number of options that were once available for custom order. Not sure if this was done for brevity in the catelogue or if the website simply has not been up-dated to reflect the changes.
For example this year they moved to a fast focus eye-piece that is the same as what you find on S&B, Zeiss, etc. it looks like they've standardized the tube diameter to 34mm, and made the EREK knob standard as well. One should call to confirm but this is how it appears in the new paper brochure. The scope you are looking at is now designated as the "ER-25".
To answer your question: how will it stand up to the recoil of a .50? I'd say you have no worries there. I had a USO SN-3 ( now called an LR-17) on a Steyr HS.50 for a bit and never felt the least bit of worry about it. In fact I'd say the scope would probably outlast the .50!

. If you have any concerns about durability go on USO's facebook page and see if they still have a video up of an SN-3 being thrown down range into the gravel then re-mounted on the gun to shoot same POI. It will absolutely sell you on their durability.
Ruggedness and durability aside, I feel there are other scopes out there that are better than the USO's in most other regards. The glass in the USO's is very good but not on the same level as S&B, Hensoldt, etc. in fact the new glass used in the Nightforce ATACR and Beast series is better than USO's glass in my opinion. The clicks on the EREK knob are not as distinct as I like to see in a LR scope, and I never liked the capped illumination control mine had. Again just my opinion.
The scary thing is they have actually become one of the most competitively priced LR scopes out there after nearly everyone else jacked their prices up for 2014. For example: S&B 5-25 PMII was $3145 this time last year, this year it is $3700 at the same dealer! This is partially due to increases from the manufacturer and partially our currency in relation to the Euro. Our plummeting dollar isn't helping things any but at least USO's pricing seems the same as it was.