Cons: if the Evans will clean and loosen any residue/scale/sand/debris after you already did a flush, you take a chance of clogging up the very small coolant passages in the oil cooler.
Keep an eye on your ECT/EOT delta, it may not happen instantly, but over time. Even if you use a coolant filter, a coolant filter is a bypass system designed to only filter 10% of the coolant at any given time.
That Con is there for Any coolant change, as altering the chemistry of your coolant system will inevitably change what gets deposited, and what gets picked up and carried around by the coolant. Especially with running flush cleaners like Restore, VC9, etc through. Those things are designed to lift off scale and residue, and yes, you attempt to flush it out as much as possible, but there will always be some left. That's why it's recommended to do your flush on the old oil cooler first, and also to run a coolant filter.
I did a complete flush, installed a filter, and ran Evans on my old cooler for a week before changing my cooler actually (my old cooler was functioning fine, it wasn't blocked, I had a 7 degree delta. I changed it because the seals around it were leaking. Figured once everything was off already, might as well). Also, the kind of Gunk that plugs up the cooler is either silicates or Glyoxal, depending on which theory you follow, not necessarily scale or casting sand. I'm more referring to it breaking down and dissolving other elements, not necessarily the 'goo'. (See analysis of coolant "GOO"......sorta
for the Glyoxal discussion and the chemical breakdown of the 'goo' found in an Oil Cooler)
I'd personally recommend running a flush, and changing to Evans on your current oil cooler as I did (as long as it's not TOO fargone. Remember, simply switching to Evans will prevent flash-boiling and pressure, your EGR cooler is now much safer, even with higher deltas, than with normal coolant), installing a coolant filter as well, run for a few days to a week, and THEN changing your oil cooler, after the Evans has run through it decently, and hopefully everything that's going to come loose, does, and gets grabbed by the filter. Is it more work? Yes, but if you do it this way, you should never need to change an oil cooler or an EGR cooler ever again.
If your oil cooler is partially clogged, there is VERY LITTLE risk of EGR Cooler rupture anymore with Evans due to the much higher boiling point, and zero pressure system. At that point I'd be more concerned about hitting Defuelling level on EOT than EGR Failure. The only reason I say VERY LITTLE, and not NO RISK, is because the EGR Cooler is the one point where the Evans could possibly even come close to hitting it's boiling point. Even so, even if it did boil, any pressure created would immediately be vented out of the zero pressure system. If you Combine Evans with an EGR Delete, you'd have pretty much rock-solid protection. If you delete the EGR, the only reason left to change the oil cooler would literally be hitting Defuel level due to it being clogged. Defuel level being around 250 degrees, which is still 120 degrees LESS than the boiling point of Evans. No risk of blowing your oil cooler.
The problem I think most people are having is you have to completely rethink how your cooling system works when you remove water from it. It now has zero net pressure across the whole system (yes, the pump will create some positive pressure on the output side, but it will also create an equal amount of negative pressure on the inlet side, net 0 pressure across the system.) No net pressure means nothing can 'blow' anymore.. 370 degree boiling point means your engine oil will actually breakdown BEFORE your coolant even comes close to it's boiling point. It literally is just a flow of liquid that circulates through your engine, and can cause little to no damage on it's own anymore.