A SplitSpectre attack is far easier to execute than an original Spectre attack. Researchers explain:

Although Spectre v1 is powerful and does not rely on SMT (Simultaneous Multithreading), it requires […] a gadget to be present in the victim’s attack surface. Google Project Zero writes in their original blog post on Spectre v1 [46] that they could not identify such a vulnerable code pattern in the kernel, and instead relied on eBPF (extended Berkeley Packet Filter) to place one there themselves.  In this point lies the strength of our new Spectre v1 variant, SplitSpectre. As its name implies, it splits the Spectre v1gadget into two parts Researchers say the second half of this improved exploitation scenario can be run within the attacker’s own malicious code, instead of the target’s kernel, simplifying the exploitation procedure.