He rather likes that extra effect of the spreader, that Ianto doesn't have as much leverage as he'd usually have. He can feel those thigh muscles working, trying to push back against his relatively slow, careful entry, and he chuckles breathlessly as he steadfastly refuses to speed up. This part is so exquisite, there's no way he's going to rush it.
At last he's fully seated inside Ianto, tight heat around his cock, and tight heat pressed against his groin too. He holds it there, partly to let Ianto adjust and partly to just let him enjoy feeling fully exactly what he's done to him. "All right?" he asks breathlessly, hands stroking lightly up and down Ianto's sides.