I've just installed Black Widow decat pipe + SC Project GP exhaust on my 750 L1.
To avoid FI you should remove the exhaust servo motor, installing a servo eliminator kit (around 45 euros here in italy).
Black Widow together with the pipes provides a small bracket to be assembled on the exhaust servo motor, in order to allow its normal operation without removing it, avoiding FI. It should work as well but I've not tried it, you just need to remove the two cables which actuate the exhaust valve.
Anyway, de-cat pipes should be used with a race filter and consequently it would be better to remap ECU to have a richer mixture in high rpms.