Use it on my 4 computers, on the laptop by the Father on the laptop of sister and on the desktop computer of sister. All had been no problems or performance degradation.
Bitdefender and Kaspersky were Tentatively installed with. Bitdefender as Freeware and Kaspersky as Jaherslizenz Norton I see with my brother on his desktop and do not understand why he does not uninstall it because it slows down too much the computer (Q6600 @ 3,1GHz and 4GB RAM, HDD).
Bitdefender flew from my computer (i7-970 with 12GB Ram, SSD) after 4 days due to very strong performance degradation. Kaspersky was similar and I was happy as the annual license had expired.
GDATA working model in the background.