Stock lifters are hydraulic on a Buell and you dont have to periodically adjust the pushrods or tappets (valve lash) Many old bikes run a solid lifter or cam follower (Triumph, BSA, Norton, Hondas, etc) and a valve lash adjustment is part of regular maintenance. Sportster style motors dont have access to the rocker arm assys without removing the top end so when running performance valve trains, you do the adjustment at the Pushrod. THATS what those telescoping pushrod covers are for.
if you dont need to adjust your pushrods (most buells) you dont need them. If you like the looks of them, the non telescoping ones are much cheaper, but im just saying,,,,,,,, all those style pushrod covers tend to leak to some degree, some a lot. Its frustrating to button up everything, get it torqued and broke in and sure enough ONE of them is leaking,, back apart again, theres 4 of them, so you have 4 opportunitys to leak, Even when sealed up they still weep when run hard or long trips.
After dealing with leaky push rod tubes for many many years, I find it refreshing to not have those issues on a Buell, which is why that smart feller Erik made them that way. Im not saying dont use them, im just saying the novelty of those style tubes wears off quick when coupled with the additional maintenance.