Last week, Mercedes caused some intrigue when its new engine chief Hywel Thomas revealed that it was battling some problems ahead of pre-season testing.
"We have got some issues with the power units," he said in a video released by Mercedes. "We know we have issues but we have plenty of plans in place to fix all of those issues. I'm sure it will all be ready for the first race."
The comments were a carbon copy of what former engine chief Andy Cowell said prior to its troubled 2020 testing programme, where Mercedes was halted several times by reliability problems.
The delayed start to the official season, which did not get going until July, proved to be a welcome boost as it gave it some breathing space to get on top of its troubles.
But although Mercedes' current cautiousness has raised eyebrows, McLaren says its early analysis of the power units has been without any snags.
Asked if McLaren has any worries about the Mercedes engines, technical director James Key said: "I mean that's obviously a question for Mercedes really. We couldn't answer that.
"To date, we have done some full scale testing on a dyno and that's been completely problem free. But I would say Mercedes are definitely the best to answer that, to be honest."
While McLaren wants to wait for pre-season testing in Bahrain to get a better gauge of any performance step it may have made as a result of its Mercedes switch, the team is already impressed with the power unit's packaging.
Key said that that factor had been a huge help in allowing McLaren to get the engine fitted in to the MCL35M amid the homologation restrictions teams are facing.
"I think the Mercedes installation is certainly extremely tidy," he explained. "You can see how much attention to detail has gone into it. It's very straightforward to package in that respect. And that has given us a few plus points.
"What has become clear over recent months is that Mercedes installation is very good to work to.
"We had to install the engine in this homologated environment, and I think working with the Mercedes colleagues, and with the power unit they're supplying us, it has made it reasonably easy to try and shoehorn this engine into an otherwise homologated car with the installation that we've had."