When you enable next-hop MPLS with the LSP metric comparison option, BGP compares the configured LSP metrics instead of a fixed metric of one to resolve the routes. This option gives the flexibility to choose a native IP path over an LSP path when they have different BGP next-hops, and the native IP path has a lower IGP cost.
After BGP resolves the next hop with LSP, it uses the LSP metric as the IGP cost for this hop. Then, all of the next hops IGP costs are compared, and only the IGP cost paths with the lowest values are considered for ECMP. When any of these paths is an LSP, then only LSP paths are taken.