In all fairness, those 3 players - Oakley-Boothe, T. J. Eyoma and Kirby - simple weren't good enough; which is why they never got games for Spurs. They are all playing in the lower divisions now.The reason why HG rules were invented was to try to get clubs to play young English/HG players as clubs tended to find it easier to buy experienced players from abroad rather than train their own youngsters (but its an idea used in other european countries with slightly different rules).
Has it worked - yes to a limited extent as there are more better quality English/HG players now than their were say 10/20 years ago. But you only need to look at Spurs to see that in last decade assorted coaches have tended to overlook the idea of some sort of focus on bringing youngsters through. To put that into context Spurs had 3 players who won the u17 world cup in 2017, but none made it through Spurs, so its not lack of quality players, but the (un)willingness of coaches to play the kids or loan them out to bring them through.
The pricing of HG players comes back to how few come through the system, through coaches unwillingness to have a plan to bring them through - itself no big surprise when you know it might take 6 years to bring a youth player through, whilst average tenure of a PL coach is about 15 months !
The site you've posted is fine. Just need to know a little about the players to make it useable - for example we have Austin and Whiteman as HG GK's but we are only likely to use one as 3rd GK, loaning the other out, so little advantage in having two of them !.
8 of the squad players are now still with an EPL club.