How valuable are Engels, Maeda & McGregor to Celtic?

Arne Engels, Daizen Maeda and Callum McGregor have been key players [SNS]Quotes attributed to Martin O'Neill over the weekend will have done little to placate Celtic fans' concerns about this summer's transfer window activity - or lack of it.Colombian striker Camilo Duran, bought from Azerbaijan club Qarabag, is the Scottish champions' only addition so far despite the veteran Northern Irishman looking to reshape his squad after nearly losing the league title to Heart of Midlothian last season.An