BiLL is right on the money,as usual.One thing I will ad is that the very first Explorers out had a thiner walled lower shaft(The one I have)and it is a little weaker than the newer rods.But with that being said,I am a very large fella,I use my detector to get up off of my knees after recovering a target,if I didn't,there would be no way I could hunt long,my knees wouldn't take it.I am not at all proud in saying that,and feel very bad for using a piece of electronic equipment like that,but I do what has to be done,for me.I broke my lower rod after using it like this for at least 6 months.Then when it broke,instead of ordering a new one,I took a piece of PVC conduit and formed it around the lower shaft where it broke and 2 ton epoxied it on.It has been like this another 6 months and still strong as ever.I know of a skinny guy that broke one using it in heavy brush and corn stubble.It does happen,but if you are thrifty,there is little down time,you can have it fixed over night.And that is if you are a tight a$$ like me and too cheap to buy another lower rod.
As far as the cracks in the housing,I have some of the worse cracks I have ever seen,and trust me,I have seen alot of explorers,and my cracks still are not what I would consider bad enough to send in and get fixed.I should,but I am going to wait till there is a foot of snow on the ground first.This is also at a critical stress point when I stand up and they have not got any worse.I have no fear ever in taking it out.I know if I go out for an all day hunt that I will have no problems.I have been told that since the cracks in the housing and lower rod are a manufactor issue,that minelab will replace them both,free of charge.Even on second hand detectors,you just pay shipping there and back.
Another point I would like to make about the so called "poor build quality",ask BiLL about this,people that I run into that think the explorer is a weak built detector,I have taken my explorer and tossed it to the ground from as much as 5 feet high and out in front of me with no problems ever.This detector is a rock,no matter what all the nay sayers say.Yea,I am stupid and ask for problems,but by God,I will have a detector that can take my abuse and keep going,and I have it.
I never have used a sov. before,except play around with one briefly,but I would think that if you are used to one,stepping up to an explorer would be cake.
I am the type of person that is never happy with anything.I have a $700 Mathews compound bow,that I love,but want a different one.I have thousands of dollars worth of guitars and basses,but want different ones.I have a 70 R/T Charger with a 440 Magnum and a 56 Chevy Bel Air 2 door,and an 86 Porsche 944 and others,but want different ones.ETC. ETC.BUT,there is not another detector made that I would get rid of my Explorer for.This is the first thing I have ever had that I have been completely happy with,and that is the honest truth.I have a CZ-5,damn fine detector,but I have not used it since the first day I used my Explorer a year ago Nov. 7th and have no desire to.
All in all,IMO,I think you should trade your CZ-7 for the Explorer and give it a whirl,I think you would be very happy with it.But,if you get it and after some time decide it is not for you,you can sell it on the classifieds here or on ebay for enough money to replace your CZ-7 with extra money in your pocket.You would not get hurt at all with that kind of trade!