My only concern is whether 29mm might be a little snug under full length mudguards - I am quite fussy and mudguard rub is something I can't stand!
It might... but it depends on the guards, actual clearances etc. But if it does rub then you can whack some 25s on (the LGG comes in 25mm too) and they'll come up about 26mm or so, which is the same as your 28 will on a narrower rim, so you'd be no worse off than you would have been really
It is so so bike/guard dependant though, I can't stress that enough, you'll clearance get variations on the same bike just by using different fittings for the same guards, let alone different guards or frames! The skill and patience of the person fitting them is important too, it's dead easy to throw a pair of guards at a bike and have them stick, but takes a bit more time and effort to do it properly and maximise clearances. I've got one bike that uses 57mm drop SP calipers and can happily swallow 30mm tyres with guards, and will even take 32s without rubbing if you're happy with very close clearance, and likewise have had other frames where getting a 25 through was a struggle, using the same brakes and guards!
Very few tyres actually come up at their rated size on 'normal/traditional' road rims, there are exceptions but it's not at all unsual for a 28c tyre to measure 25-27mm on a traditional dimensioned road rim like an Open Pro. Older touring rims and modern road rims with bigger internal widths are normally the only way to actually get the full width. It's very telling when you actually go and start measuring real widths with a vernier on various rim and tyre combos.
Also worth noting that the LGG is somewhat of an underappreciated star IMO, I don;t like to generalise too much about tyres as individual use and local conditions can mean experiences vary wildly but IME the 120tpi versions are very comfy, very quick in real life* (despite not doing great on the infamous bicyclerollingresistance website) and decently robust, and the 60tpi versions are way better than they have any right to be for such a 'basic' tyre. I've put about 2000 miles on the 120tpi casings so far and very happy, probably only 1000-1500 on the 60tpi variants so a bit early to draw long term conclusions but so far I've been impressed.
*not quite 4000s or Turbo Cotton quick, but pretty damn close and seem to be more robust in terms of tread thickness and PP.
