Few things of note.
I would be cautious about that trade for the mp40. Is it also QD? MFG date? Are the bearings worn and it's noisy, etc? It could just be that they are downsizing, but be cautious and be discerning

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Secondly, if it were apples to apples and you were planning on getting a larger tank in the future, a mp40 is a great idea. You can always turn the flow down and it's ready for your upgrade in the future!
Last, you may get away with one mp10 plus return depending on what you're stocking. Honestly, I would start with one mp10 (or your trade for your mp40) and post a video of your flow or watch videos to compare. You'll likely want two mp10s if you're running sps, but that second one can be bought later (plus you can wait for a good deal). Since you're just starting out, one mp10 will be plenty fine at first and you can buy the second pump once you start stocking corals if the need arises. No use in getting fantastic flow if it's still at the planning/box of rocks stage in my opinion