peugeot/citroen diesel engin timing belt tension?

hav got a berlingo wit the dw8 engin fitted havin come from a long line of pugs with xud lumps in them belt setup has always been easy . but the haynes book of errors states use of a gismo that electronicaly senses belt tightness , all indipendent garages hav not heard of it /dont use it only dealers use it / myself cant seem to get one, so my question is how important is this ULTRA ACURATE method of setin up belt tension or can i as lernd at night school as used on cortinas of long ago twist at longest run a third and hope for the best . also cud it be a good idea not to let the belt do the recomendid 80000 miles and cut it down to 50000 to be safe on a less acurate method . cheers lee