What do you think Neil??
Its pretty similar to alot of other cages ive done like Ryan's
This one has the full roof X, different head support bars, intrusions and the windscreen supports.
The U type intrusions have a few advantages, the X bars obviously have a raised stress area where they are welded. The welded sections meet at fairly acute angles usually 50+ degrees, that leaves plenty of welded surface area, the welded area is just as strong as the original tube but the heat zones around the area can become a problem.
If they fail the X bars usually split open and create all sorts of nasty sharp edges etc not to mention the lack of protection.
The U bar obviously has no welded areas. It is also double tube diameter the entire length of the intrusion as opposed to the X bar which has a section usually an inch or so long that is only single bar protection.
For the U bars to fail they either need to spilt open (they are made from 750Mpa CDS as opposed to 350mpa), tear the welds off the main hoop and front legs (they are also tagged to the sill pannels and pillars where possible so not just relying on the hoop and leg welds in Neil's case) or finally they need to bend the legs and hoop, also needs to bend the hoop X, dash bar and roof supports to do so though...
So the U bars are stronger when done properly in double tube and they remove the chance of the X bars intersection failing.
The disavantage of the U bars is the additional work it requires. A normal X intrusion is pretty simple, straight tube two knotches, typically the cut tube is a 55-60 degree knotch welded together where it intersects and move on. sometimes fit two vertical gusset tubes if required.
The U bars need to be thought out alot more to make sure the bends line up and butt up against the other tube,it looks awful if the bends are different radius' or angles too so some though has to go into that too. I flatten the bend where they meet and MIG weld the two bars around the circumference, then make up two vertical supports from offcuts, finally cut the gusset plates and weld them in and with neil's car linish it all smooth so the whole gusset looks seamless to the intrusion.
Its easy to spend 3 hours on an intrusion bar. Worth the time though if the owner is willing to pay for it.
I rarely do U bars due to the extra time and cost involved. Not many people really bother either.