Difficult to say, primarily because of the twin aspect, i.e. every comment that gets made about them is in relation to the other Twin.
Ben is without a doubt the more talented of the pair, that's why he's first choice alongside Grant Gilchrist, and Alex was kept outside the best 23 by former Shark Anton Bresler.
But he's got the skillset to potentially translate into a good Super Rugby Player. He had his best NH season too, despite having little support at times in the locking department (due to injury) and clearly was "homesick".
It seems a good moneyball signing tbh. He still has quite a high ceiling, and 2 years gives him a bit of time to chase it. But if the best of the current crop of available locks are all looking to sign elsewhere (Matwijow, Phillip etc.) and we don't rate the group behind them, he should be more than capable of holding down positions before we can develop an U20s boy or chase someone OOC overseas/domestically (e.g. Trevor Hosea, Hugh Pyle and say Blake Enever)