I am currently play a necromancy wizard in a long DND campaign. My character is lvl 6 and just got the main class feature that allows for stronger summons

I was wondering if multiclassing 1 lvl into death cleric was worth delaying most of my wizard features and spells by 1 lvl. I don't see a lot of use in the lvl 10 wizard feature for my character so the main contention is getting access to 4th and 5th wizard spells 1 lvl later 

Death cleric would give me an immediate boost of proficiency in some armour and shields, access to a few handy 1st lvl cleric spells and Reaper that allows necromancy cantrips to hit 2 targets within 5 feet of each other (Very strong in my opinion)

My characters current play style is summoning Zombies to support the tanks and using concentration to cast buff spells (haste, enlarge etc). Its because of this i find myself casting cantrips a lot so i thought reapers would be really strong as it basically doubles their effectiveness in a lot of cases 

I think it makes sense for your build... both mechanically and within the idea of a necromancer character.

I'm in favor of staying in wizard, mainly because death domain is designed for villains and as such is intentionally overpowered. Mechanically and thematically, it fits perfectly. However, I have to say that death domain was not meant for PCs

I think that's a good point, but a single level dip to give a player more versatility while their other spells are focused mostly on concentration spells is more fair than diving fully into the class.

I have done this dip for the exact same reasons on a warlock.  As you already point out the spell progression is the biggest problem here.  The only other one, is without knowing what your INT vs. WIS you might hurt yourself on the necromancy cantrip as far as the final attack bonus (chill touch) or save (Toll the Dead) if the stats are significantly different.

Otherwise, enjoy the dip.

Talk to your DM to make sure they even allow Death domain...the class was designed for NPCs/villains, as DKMagic said, and I personally would not allow it in my game. I'd also consider the thematic implications of becoming a cleric, such as what god you serve and what hierarchy you obey. All in all, sticking with wizard seems like the easiest way to go.

Quote from NaivaraArnuanna >>

Talk to your DM to make sure they even allow Death domain...the class was designed for NPCs/villains, as DKMagic said, and I personally would not allow it in my game. I'd also consider the thematic implications of becoming a cleric, such as what god you serve and what hierarchy you obey. All in all, sticking with wizard seems like the easiest way to go.

So taking nothing away from this (the DMs Call); one of the oddball things is that in the case of Forgotten Realms, this isn't quite true.  Because per the PHB and SCAG,  Kelemvor's only valid domain is the Death Domain, and he's LN, not evil. 

He isn't given access to the grave domain, unless you have XGtE, which might be more appropriate, but is 100% based on what the DM has/supports.

The Death Domain is an additional domain choice for evil clerics, and the Oathbreaker offers an alternative path for paladins who fall from grace. A player can choose one of these options with the your approval.

Typo aside, there's no warning here that the choices are overpowered or not designed with PC balance in mind. There can certainly be RP/alignment issues, but no more than Necromancy.

The extra target thing seems really strong, but it's one of those things that isn't in actual play. There's not always another adjacent target, sometimes you're fighting stuff where necromancy cantrips are worthless, half the time the extra attack misses anyway, etc.