Personally feel like there may be a little more with Zinchenko than Tielemans. Tielemans has been a solid player for a few years, but....
Zinchenko helps us shore up our midfield, and provide cover for Tierney at LB. He's also younger, and doesn't have many miles on him. Actually seems to me he'd be a decent starter that we can improve upon (via Viera or other signings), while covering Tierney and next year letting us move on from El Neny as CM cover.
Nothing to get really excited by, but I'm not sure Tielemans is either.
Seems like a smart buy for under 35m as long as there's other quality coming in.