You're welcome to do that, it helps.

欢迎您这样做， 它会有所帮助。

But you're welcome to do so.

但你想做的话可以随意。

… then they are 'welcome to do so'. Just watch out where you stick it! I suppose, as long as you respect other visitors and don't get in the way, then it's ok to use one.

他们完全可以使用。只需要小心自拍杆伸出去的位置！我想只要你尊重其他的参观者，不挡路，用自拍杆可以接受。