In this case it is the technology that matters. Each of those companies are tech companies first and foremost, and while Integral does offer their own packaged liquidity (which you can get direct from a bunch of brokers: FXCMpro, AXI, Pepperstone, Sucden, etc) Currenex needs to be sourced from a partner either a PB, LP, or bank.
In most instances you will not get better tier sizes, pricing, or spreads when you deal yourself or through a small third party.
Everyone likes to think the brokers are here to kill the retail trader but in some cases, especially when it comes to quality of liquidity, a broker is your best bet.
Also the bridge you are using is a VERY important aspect, and if you are only sourcing liquidity from one source the amount of off quotes and similar issues may be higher as you have no filtering mechanism in place and without the ability to add custom rules to the bridge, well you aren't really any better off.