Final reserve (30 minutes at 1500') in an NG is right on the 900kg mark, so they were very close to landing with final reserve intact, after three approaches and a diversion. Missed approach, and quick vectors for a second approach in an NG is about 500 kg, a visual circuit about 250-300kg.
No criticism can be made without knowing the circumstances of the diversion - what route was planned versus what they were able to get on the day, and the planned destination weather vs. what actually was involved.
Frankly it all sounds normal, "efficient" minimum planning for convective weather forecast @ destination. Take 1000ks over plan for the convective weather, arrive & make a missed approach - be offered a second approach to a reciprocal runway (command decision time when you calculate you just have enough fuel to achieve this and still divert) take the second approach, unfortunately make another missed. Two weather missed approaches = mandatory divert in most SOPs.
Then the diversion runs a touch longer than anticipated or planned, resulting in a landing a smidge under fixed reserve - an honest Mayday call required by SOPs when this becomes the case is transmitted (again a good, honest, command decision when some might have remained silent).
Tight fuel planning, unlucky on the day, a couple of difficult decisions reasonably handled (and again unlucky with the second approach), and it all working within 100kg of being OK. Tough day out, I think.