rabbut
I don't bite, all that often...
It won't touch the Eheims filteration capabilities, but the extra is better than no second filter to help.
The 2028 and the XP3 would IMO be better than a FluvalFX5, as your proposed twin filter combination offers a redundancy against failures. The FX5 is unporoven remember, earlyer than expected failures of this piece of hardware are not yet out of the question. For now, I'd go with an XP3 and a 2028 If you can save for a while for two 2080's then that would be better, but the combination of Eheim and Rena is a good compromise The FX5 is a riskier option as of yet, especially considering Fluvals track record, or more to the point lack thereof.....
HTH
Rabbut