I have had quite a few bits & pieces from Prestige & they are very good, although I haven't had either of those kits, the PRMRP Hymek conversion kit is more comprehensive as it contains much more cosmetic details than the Prestige kit , I think the Prestige kit concentrates mainly on motorising the Triang loco . I would price up the total project first though as I have known S/H Heljan Hymeks go for around the ?200 mark.
I've built one of their 08 kits and it's not bad and builds up well , a bit of care is required forming the bonnet ......it's a bit 'old technology' when compared with the MMP kit of same but it's cheaper than the latter so it's a case of 'you pays yer money and takes yer choice' .