If your alternative is signing a couple of 2 star lineman that have say a 5% chance of being great, 15% chance starter, 20% 2-Deep Contributor, 60% chance of not contributing at all, why would you not take a chance on trying to mold these physical specimens into football players.
With Langi and Tu' ungafase I think your chances of success are much better. It is probably a 20% chance of being great, 40% chance of being starter, 10% 2-deep contributor and 20% not contributing at all. You may disagree with my percentages, but I think these guys have 2-3 times the chance of being at the least solid contributors compared to some of the last minute offers we have made to marginal players in the past several years.
It may be quite a learning curve for them, but you can't teach size and athleticism and these guys have the chance to be great for us if the coaches can train them up. You may not be able to go out and get 20 of these guys every recruiting class because coaches can't be teaching 20 guys the basics of football each year, but taking a risk on 3 guys a year is a great strategy to really elevate the program. Having just 2-3 dominant players a year at key positions can really elevate a program and gambling on physical specimens like this is more likely to get those physically dominant players.