It's not hard to see the club's sense behind the move. Low risk, given his solid performances since joining Roma years ago (and a solid shift last season where he would play under Inzaghi, outside of his natural position). Total cost of 12m including wages and transfer fees (excluding any possible agent fees). Maintains a certain technical level and meets expectations for a squad that is competitive for top 4 football without spending a lot of money. We need midfielders, he suits Inzaghi ball, and Inzaghi probably wants more players with his ability to dictate play in the squad. Thus it becomes a short term boost to our short term goal of Champions League football to keep the club as afloat as possible.
But it's also not hard to see how easily this move can go wrong. I know Marotta's strategy has always revolved around low risk Serie A acquisitions and mixing veterans with young talent. But this all assumes that Mkhi's on the pitch contribution will compensate for the wages we will spend on an asset with no resale value whatsoever. It's reported the difference between the two offers is that Inter is offering a 2 year deal vs Roma offering 1 year. At his age, physical decline is a huge risk. He's not injury prone but just recently came off a 3-4 week injury which was relapsed 15 minutes into the ECL final. If he declines in any way it makes the deal a flop for Inter.
If we are seeking Mkhi as a bench option to add depth, by default I'm against signing older players as bench options because it becomes more difficult as you age to stay fit without playing regular football. Making the level of his physical condition even lower in addition to the possibility of natural decline. Also, Mkhi is no super-sub or workhorse who you can just sub in to grind away to have some effect on the last 20 minutes of the match. To me he is the kind of player who needs time to settle into the rhythm of a game.
Other than that (making him a sub by default), it's not the worst transfer in the world but it doesn't give any excitement to the fans. What I fear is that the club is planning to sell Hakan and this is his replacement, à la Džeko.