i have researched electronic leak testers up down and sideways and the absolute best was the yokahama /Bacharach
http://www.bacharach-inc.com/h10g.htm
however it's quite dear and not that 'handy'
however this model seems closer-
http://www.bacharach-inc.com/h10xpro.htm
I bought one of these from Bacharach uk in leamington spa in when I needed to get something decent for an engineer checking a couple of carrier chillers retro'ed to 407c which leaked
however my personal favourite way is still a wee dram of R22 and 500 psig nitrogen and the trusty old 'blue' flame-yes,yes I know but it NEVER fails to find the leak ¬!!
cheers
richard