The CEO of XL Group P.L.C. is “delighted” with the state of the combined entity created by XL’s $4.28 billion acquisition of Catlin Group Ltd. a month after the deal closed.

And analysts agree that the deal appears to be working well.

“So far so good,” said Meyer Shields, managing director at Keefe, Bruyette & Woods, Inc. in Baltimore. “They have had an extended amount of time to plan out every step of it.”

The deal, originally proposed last December, officially closed May 1. The acquisition of London-based Catlin by Dublin-based XL created an insurance powerhouse, with the marketing name of XL Catlin, writing nearly one-tenth of Lloyd’s of London business.

In a conference call Thursday, Mike McGavick, CEO of XL, said the “synergy benefits” of the acquisition should lead to about $250 million in savings, up from an original $200 million estimate.

The savings will be achieved through reducing personnel overlap, process improvement, systems-related actions, such as the ability to retire existing systems or to end investment in new systems that are being replaced by legacy systems, and in the areas of facilities, Mr. McGavick said. He added that the savings have tended to arise from process- and systems-related actions.

Mr. McGavick said that “everything for us is about speed” in completing the transition and becoming entirely outwardly focused. “The next couple of months is when we start to see colleagues leave — that's a painful experience,” he said.

Nonetheless, “we are delighted with where we stand,” he said.

“There are always potential difficulties in integrating companies, but I think it sounds like from what they said things are going well, and it’s still relatively early,” said Brian Schneider, senior director of insurance at Fitch Ratings Inc. in Chicago. “I think they’ve had a head start, and I think a lot of that is owed to the fact that it’s an extremely friendly deal.”

Mr. Schneider noted that Mr. McGavick and Stephen Catlin, former CEO of Catlin Group and now executive deputy chairman of XL Catlin, came together “with their mutual respect for each other and looking to create this larger entity. I think there was a lot of thought put into the integration of these two entities.”

“We’re still cautious on how it will all play out,” Mr. Schneider said. “We’ll watch and see how the integration continues and get into the midyear renewal periods. At least on paper, it looks like it’s working out as well as could be expected.”

Mr. Shields said he thinks Mr. McGavick’s savings estimates are “conservative,” adding there is “no upside to overpromising.”